Chapter Summaries

Key Plot Points and Events

• Mei survives a powerful flame attack, which surprises Yuyuko, who admires Mei's strength.
• Hiyamaru and Crimson Crow's Wing praise Mei excessively, causing Mei to feel embarrassed.
• Yuyuko mentions a friend named 'Purple', who Mei assumes is Yukari Yakumo, a powerful gap yokai from Gensokyo.
• Yuyuko reveals that 'Purple' exists in this world but cannot enter it, hinting at a connection between the worlds.

Character Developments

• Mei gains confidence in her abilities after surviving the flame attack.
• Yuyuko shows admiration for Mei's strength and reveals her past friendship with 'Purple'.
• Hiyamaru and Crimson Crow's Wing display their loyalty and desire to please Mei.

Significant Themes

• Strength and survival: Mei's ability to withstand the flame attack highlights her power and resilience.
• Friendship and past connections: Yuyuko's reminiscence about 'Purple' emphasizes the importance of friendship and shared history.
• World connections: The mention of 'Purple' and Gensokyo suggests a link between the worlds, hinting at a larger universe.

Character Interactions

• Yuyuko admires Mei's strength and compares her to 'Purple'.
• Hiyamaru and Crimson Crow's Wing praise Mei excessively, causing her embarrassment.
• Youmu reminds Yuyuko of 'Purple's' sensibilities, showing her awareness of Yuyuko's past.
• Mei shows curiosity and caution when learning about 'Purple', suggesting her interest in the world's connections.

Key Plot Points and Events

• Yuyuko and Youmu, along with the White Jade Palace, accidentally crossed over from Gensokyo's Underworld to the Underworld of the current world.
• They survived the Feather of Ruin Unleashed (Tianhuo) by crossing the Sanzu River using a ferryman controlled by Yuyuko's power over the undead.
• Mei, Yuyuko, Youmu, and Crimson Crow's Wing prepare to cross the Sanzu River to reach the mortal realm.

Character Developments

• Mei understands the situation and is relieved that Yuyuko and Youmu are present.
• Yuyuko maintains her composure and optimism despite the unexpected situation.
• Youmu demonstrates honesty and knowledge about the Underworld's rules and ferrymen.

Significant Themes

• Power and Control: Yuyuko's power over the undead allows her to control the ferryman and cross the Sanzu River, highlighting the importance of her role in managing the Underworld.
• Adaptation and Resilience: Characters adapt to unexpected situations, showing resilience in the face of chaos and danger.

Character Interactions

• Mei and Yuyuko share a conversation, leading to Mei's understanding of their situation.
• Youmu explains to Crimson Crow's Wing how they survived Tianhuo, showcasing honesty and trust among the group.
• The group prepares to cross the Sanzu River together, emphasizing their unity and shared goal.

Key Plot Points and Events

• The group travels on a boat through the Sanzu River, followed by grotesque water ghosts that can't attack unless someone falls into the water.
• Mei asks Yuyuko if she can control the water ghosts, but Yuyuko declines due to the ghosts' corrupting nature.
• Hiyamaru offers to control the ghosts, but Mei declines due to the risk of contamination.
• Mei introduces Hiyamaru as a specialty of Yae Village, humorously describing her as an "ingredient" to tease Yuyuko.

Character Developments

• Mei: Shows concern for her sisters' safety and well-being, displaying a protective side.
• Yuyuko: Reveals her desire for Hiyamaru, showing her playful and greedy nature.
• Hiyamaru: Demonstrates eagerness to help and prove herself, showcasing her confidence and resilience.

Significant Themes

• Safety and Protection: Mei's concern for her sisters highlights the theme of protection and ensuring everyone's safety.
• Risk vs. Reward: The decision not to let Hiyamaru control the ghosts explores the idea of weighing potential risks against rewards.
• Humor and Teasing: Mei's introduction of Hiyamaru as an "ingredient" brings humor and lightheartedness to the scene.

Character Interactions

• Mei and Yuyuko: Mei's teasing of Yuyuko shows their playful sisterly bond, while Yuyuko's reaction highlights their shared sense of humor.
• Mei and Hiyamaru: Mei's protective behavior towards Hiyamaru strengthens their bond as sisters.
• Yuyuko and Hiyamaru: Yuyuko's reaction to Mei's introduction of Hiyamaru hints at a potential playful rivalry between them.

Key Plot Points and Events

• Mei and her group successfully escape the Underworld and return to the Human World.
• They are greeted by Yōki, Yingcao, and Hiyoumaru at an inn.
• Mei decides to discuss their plans in private due to the attention they're drawing.

Character Developments

• Mei: Shows concern for her companions' safety and discretion, indicating her growing maturity and responsibility.
• Hiyamaru: Struggles with feelings of inadequacy and jealousy, as she feels overshadowed by Hiyoumaru and sees herself only as food to Yuyuko.

Significant Themes

• Identity and Self-Worth: Hiyamaru's struggle with her self-image and her fear of being seen as just an ingredient highlights the theme of self-worth and identity.
• Bonding and Belonging: Mei's concern for her companions and their reunion at the inn emphasizes the importance of bonds and belonging.

Character Interactions

• Mei and Yuyuko: Mei's protective behavior towards Yuyuko shows their close bond and Mei's growing leadership role.
• Hiyamaru and Hiyoumaru: The sisters' dynamic showcases sibling rivalry and Hiyamaru's insecurities, which may lead to further conflict.
• Mei and her group: The reunion at the inn highlights the group's camaraderie and Mei's role as the leader, with everyone eager to hear her plans.

Key Plot Points and Events

• Mei returns to her room, acting casually and unladylike.
• Hiyamaru and Hiyoumaru, two fox girls, argue over their appearances and roles.
• Mei threatens to turn them both into foxes if they continue arguing.
• Hiyoumaru reports an incident involving a bath spirit targeting Princess Ying Ji.

Character Developments

• Mei: Shows dominance and assertiveness in managing her fox companions.
• Hiyamaru: Feels threatened by Hiyoumaru's resemblance to her and her closeness to Mei.
• Hiyoumaru: Recovered some of her power and refuses to remain a fox, asserting her independence.
• Princess Ying Ji: Remains calm and composed despite the bath spirit incident.

Significant Themes

• Power dynamics and dominance (Mei's control over her fox companions).
• Identity and self-image (Hiyamaru's distress over Hiyoumaru's appearance).
• Protection and responsibility (Mei's concern for Princess Ying Ji's safety).

Character Interactions

• Mei asserts her authority over Hiyamaru and Hiyoumaru, ending their argument.
• Hiyamaru and Hiyoumaru express their differing views on their appearances and roles.
• Mei shows concern for Princess Ying Ji's well-being, inquiring about her safety.

Key Plot Points and Events

• Mei, Yōki, and Yingcao encounter a bath spirit yokai, which Yingcao accidentally defeats by flailing around in fear.
• Mei introduces Yuyuko and Youmu to the group.
• Mei takes everyone to a restaurant for a meal.

Character Developments

• Yingcao: Yingcao displays immense physical strength but lacks courage and understanding of her own abilities.
• Mei: Mei shows kindness and responsibility in taking care of her friends and keeping her promises.
• Hiyoumaru: Hiyoumaru shows jealousy towards Mei's new friends, hinting at her growing feelings for Mei.
• Hiyamaru: Hiyamaru remains protective of Mei and disapproves of Hiyoumaru's jealousy.

Significant Themes

• Friendship and Loyalty: Mei's actions demonstrate her commitment to her friends and her willingness to support them.
• Courage and Self-awareness: Yingcao's lack of courage and understanding of her own strength highlights the importance of self-awareness and bravery.

Character Interactions

• Mei and Yingcao: Mei praises Yingcao for her actions but realizes Yingcao needs help overcoming her timidity.
• Hiyoumaru and Hiyamaru: Hiyoumaru's jealousy leads to tension with Hiyamaru, who remains protective of Mei.
• Mei and Yuyuko: Mei keeps her promise to Yuyuko, showing kindness and consideration towards her.

Key Plot Points and Events

• Mei treats the group to a lavish meal, satisfying Yuyuko's insatiable appetite.
• Mei announces a day of rest before departing for Kyoto the next morning.
• The group encounters yokai on their journey but passes through smoothly.
• Upon reaching Kyoto, they find it transformed into a Magic City with dense demonic energy and resentment, and the Dragon Vein has disappeared.

Character Developments

• Yuyuko's eating habits and financial strain on the White Jade Palace are highlighted.
• Youmu expresses gratitude towards Mei for her financial resources, implying past struggles.
• Mei's mission to eliminate Hagoromo Gitsune and deal with the evil Seimei is clarified.

Significant Themes

• Wealth and its influence on survival and well-being (Yuyuko, Youmu, Mei).
• The transformation of Kyoto into a Magic City and the shift of power from Kyoto to Edo reflect the impact of supernatural forces on society.

Character Interactions

• Mei and Yuyuko: Mei ensures Yuyuko's appetite is satisfied, showing care and provision.
• Youmu and Mei: Youmu expresses gratitude towards Mei for her financial resources, implying a potential change in their dynamic.
• The group: They travel together, facing yokai encounters, and share experiences, fostering camaraderie.

Key Plot Points and Events

• The birth of the Child of Darkness, a new yokai king, is celebrated in Kyoto.
• Hagoromo Gitsune, a powerful yokai, plans to destroy the human world and create a new yokai world starting from Kyoto.
• Yokai from various regions gather in Kyoto to pay homage to Hagoromo Gitsune or witness the event.
• Nura Rikuo and his group arrive in Kyoto in the evening, witnessing the Hyakki Yagyō (Night Parade of a Hundred Demons) led by different yokai factions.

Character Developments

• No significant individual developments in this chapter.

Significant Themes

• The power dynamics and hierarchy among yokai.
• The dependence of certain yokai on human fear for their existence and strength.
• The concept of Hyakki Yagyō as a display of power and a means to instill fear in humans.

Character Interactions

• No significant interactions among characters in this chapter.
• The chapter focuses more on describing the scene and the nature of yokai in Nura Rikuo's world.

Key Plot Points and Events

• Oni-harai's next stage, "Oni-gari," is introduced, allowing it to use fear as an attack.
• The Hyakki Yagyō's second function is revealed: the leader absorbs the power of the hundred demons, gaining "Ougyo," a terrifying and special power.
• Kyoto city is filled with powerful Great Yokai, with over seventy percent of the Eastern Seas' Great Yokai gathered there.
• Mei decides to enter Kyoto, despite the chaos and danger.

Character Developments

• Yingcao feels pressured by the demonic energy in Kyoto, showing her timidity.
• Mei exhibits leadership and concern for her group, wanting to build Yingcao's courage.
• Hiyoumaru expresses her frustration at always being the one to protect others, revealing her desire for fairness.
• Princess Ying Ji feels guilty for being a burden, showing her self-awareness and kindness.

Significant Themes

• Power dynamics among yokai, with most being part of factions due to the strength of Hyakki Yagyō leaders.
• The impact of fear on both yokai and humans, as seen through Oni-harai's "Oni-gari" and the general chaos in Kyoto.
• The importance of courage and facing one's fears, as seen through Mei's desire to build Yingcao's courage.

Character Interactions

• Mei shows concern for her group, wanting to help Yingcao build courage and chiding Hiyoumaru for upsetting Princess Ying Ji.
• Hiyoumaru expresses frustration at her role in protecting others, leading to a misunderstanding with Princess Ying Ji.
• Princess Ying Ji feels guilty for being a burden, showing her kindness and self-awareness.
• Yingcao expresses her timidity and lack of confidence in protecting Princess Ying Ji.

Key Plot Points and Events

• Mei tasks Yingcao with protecting Yōki from yokai who seek her heart, comparing Yōki to the Sacred Jewel from Inuyasha's world.
• Yingcao expresses her inability to protect Yōki due to her past failures and fear of losing another friend.
• Mei decides to enter Kyoto with the group to protect Yōki herself, despite initially wanting Yingcao to train by guarding Yōki.

Character Developments

• Yingcao: Struggles with self-doubt and fear of failure, leading to emotional outbursts.
• Mei: Shows concern for Yingcao's feelings and adjusts her plan to protect Yōki after seeing Yingcao's distress.

Significant Themes

• Self-Doubt and Fear of Failure: Yingcao's past experiences and fear of losing Yōki cause her to doubt her abilities.
• Protection and Responsibility: Mei's initial plan to have Yingcao protect Yōki and her later decision to enter Kyoto with the group highlight the theme of taking responsibility for others' safety.

Character Interactions

• Mei and Yingcao: Mei shows understanding and empathy towards Yingcao's emotional state, adjusting her plans to accommodate Yingcao's feelings.
• Yingcao and Yōki: Yingcao's fear of losing Yōki, similar to how she lost her previous friends, drives her emotional response to Mei's request.
• Youmu's Intervention: Youmu offers to protect Yōki after seeing Yingcao's distress, showing concern for both Yingcao and Yōki's well-being.

Key Plot Points and Events

• Mei and her group enter Kyoto, the vast imperial capital controlled by Hagoromo Gitsune.
• They hear human screams and find yokai hunting humans, indicating the city's dire situation.
• Mei decides to intervene, not out of saintliness, but due to her capricious nature and desire to understand Kyoto's dynamics.

Character Developments

• Mei: Shows curiosity about Asai Chacha and Hagoromo Gitsune, and her willingness to help humans despite not being a saint.
• Crimson Crow's Wing: Demonstrates loyalty and concern for Mei's safety by alerting her to the human screams.

Significant Themes

• The power struggle between humans and yokai, with Hagoromo Gitsune controlling both worlds.
• The historical infamy of Asai Chacha, similar to Daji, due to her possession by a nine-tailed fox.
• Mei's capricious nature and her complex motivations for helping others.

Character Interactions

• Mei and Crimson Crow's Wing: They work together, with Crimson Crow's Wing providing information and Mei making decisions based on her curiosity and whims.
• Humans and Yokai: The humans are under threat from the yokai, highlighting the power imbalance and danger in Kyoto.

Key Plot Points and Events

• A group of humans are chased by yokai (supernatural entities) through a narrow alley, with the yokai enjoying the humans' fear and terror.
• The humans, in their panic, exhibit selfish and cruel behavior to escape, including pushing others, injuring companions, and abandoning family members.
• A mother and daughter are trampled and left behind, with the mother embracing her daughter to protect her from the approaching yokai.
• The most powerful yokai, a Kottou-onna (a vengeful spirit from Eastern Sea legends), leads the chase along with other yokai like Akagashira, Ashikubi, and Onibi-onna.
• Mei, the protagonist, arrives with her companions just as the Kottou-onna is about to attack the mother and daughter, along with a young man trying to help them.

Character Developments

• The humans display their ugly side in their desperation to survive, showing selfishness and cruelty.
• The mother demonstrates love and protectiveness towards her daughter, even in the face of death.
• The young man trying to help the mother and daughter shows kindness and bravery.
• Mei, the protagonist, is positioned as a potential savior, arriving just in time to intervene.

Significant Themes

• The darker side of human nature under extreme circumstances.
• The power dynamics between humans and yokai, and the breaking of the agreement that humans are safe within their homes at night.
• The theme of protection and love, as seen in the mother's actions towards her daughter.

Character Interactions

• The humans interact cruelly with each other in their desperation to escape.
• The mother and daughter interact with love and protectiveness towards each other.
• The young man interacts with the mother and daughter, showing kindness and willingness to help.
• Mei is about to interact with the Kottou-onna and the other yokai, positioning herself as a protector of the humans.

Key Plot Points and Events

• Mei protects Yōki, the little girl, and her mother from the Kottou-onna (a powerful yokai) using her Fire Fairy Type II gun and lightning-enhanced tachi, ultimately defeating the yokai.
• Mei expresses concern for the little girl's mother, who is injured, and promises to have her treated by her physicians.

Character Developments

• Mei demonstrates her combat prowess and willingness to protect the innocent, showing her heroic nature.
• The little girl displays courage and maturity beyond her years, expressing admiration for Mei.

Significant Themes

• Protection and Heroism: Mei's actions highlight her desire to protect the innocent, showcasing her heroic qualities.
• Courage in the Face of Fear: Both Mei and the little girl exhibit courage, with Mei facing the yokai fearlessly and the little girl showing no fear towards Mei despite the brutal yokai defeat.

Character Interactions

• Mei and Yōki: Mei shows kindness and concern for Yōki, gripping her hand for comfort and asking for her help in saving the others.
• Mei and the Little Girl: Mei shows affection towards the little girl, patting her head and promising to help her injured mother, while the little girl admires Mei's strength and kindness.
• Mei and the Injured Mother: Mei expresses concern for the mother's injuries, promising to have her treated by her physicians.

Key Plot Points and Events

• Raiden Mei and her group encounter a woman injured by being stepped on. Yōki heals her, demonstrating her healing abilities.
• The woman and her daughter express gratitude to the group, but the woman is cautious due to their noble attire and the power dynamics in the Eastern Seas.
• Raiden Mei decides to eliminate a nearby hundred demons organization and splits her group to tackle the mission more efficiently.

Character Developments

• Yōki: Confirms her healing abilities and expresses happiness in helping others.
• Raiden Mei: Shows concern for Yōki's feelings and understanding of her abilities, while also demonstrating her leadership and strategic thinking in handling the mission.
• The Injured Woman: Exhibits caution and restraint due to her low social status and the power dynamics in the Eastern Seas.

Significant Themes

• Power dynamics and social hierarchy in the Eastern Seas, with commoners holding little value compared to nobles and samurai.
• The importance of teamwork and strategic planning in missions, as shown by Raiden Mei's decision to split the group.

Character Interactions

• Raiden Mei and Yōki: Mei allows Yōki to heal the woman to boost her confidence and understanding of her abilities.
• Raiden Mei and Hiyamaru: Mei declines Hiyamaru's request to join her team, emphasizing the importance of Hiyamaru's own mission and growth.
• The Injured Woman and Raiden Mei's group: The woman expresses gratitude but maintains caution due to the group's noble status and the power dynamics in the Eastern Seas.

Key Plot Points and Events

• Mei leads Yōki and Ying Cao into a dark, deserted alley at night, where they're surrounded by malevolent yokai.
• The yokai, attracted by Mei and Yōki's human beauty, disregard their leader's rules and attack, aiming to consume their livers to gain power.
• Ying Cao, being a yokai herself, is ignored by the others.

Character Developments

• Yōki and Ying Cao show fear and rely on Mei for protection.
• Mei remains calm and composed, showing no fear despite the danger.
• The yokai display their ruthless nature and disregard for rules in the face of temptation.

Significant Themes

• The allure and danger of human beauty to yokai.
• The corrupting influence of power and temptation.
• The disregard for rules and hierarchy in the face of desire.

Character Interactions

• Mei, Yōki, and Ying Cao cling to each other out of fear and for protection.
• The yokai interact by arguing over who gets to consume Mei and Yōki, disregarding their leader's authority.
• The dynamic between human girls and yokai is explored, with the humans being seen as desirable prey rather than potential mates.

Key Plot Points and Events

• Mei, a powerful samurai, faces a horde of yokai (supernatural creatures) to protect Princess Ying Ji and Yingcao.
• Mei entrusts Princess Ying Ji's protection to Yingcao, handing her a sword, and charges at the yokai.
• Mei leaves a protective curse seal on Princess Ying Ji and intentionally lets some yokai approach them to test Yingcao's resolve.

Character Developments

• Mei: Demonstrates confidence and strategic thinking in protecting the princess. She reveals her powerful authorities, including "resurrection," showing growth in her abilities.
• Yingcao: Struggles with self-doubt and anxiety but steps up to protect Princess Ying Ji when faced with the yokai threat. She shows potential for growth as a protector.
• Princess Ying Ji: Remains calm despite the danger, observing the situation and the characters around her.

Significant Themes

• Protection and Responsibility: Mei entrusts Yingcao with protecting the princess, highlighting the theme of responsibility and growth.
• Facing Fear: Both Yingcao and Princess Ying Ji face their fears and anxieties when confronted by the yokai.
• Power and Confidence: Mei's display of power and confidence contrasts with Yingcao's self-doubt, highlighting the theme of power dynamics.

Character Interactions

• Mei and Yingcao: Mei tests Yingcao's resolve and forces her to confront her fears, pushing her to grow as a protector.
• Yingcao and Princess Ying Ji: Yingcao struggles to protect Princess Ying Ji, leading to a tense dynamic between them as Yingcao grapples with her self-doubt.
• Mei and the Yokai: Mei demonstrates her power and dominance over the yokai, instilling fear and respect in them.

Key Plot Points and Events

• Yingcao, despite her fear, steps in front of Yōki to protect her from four mid-level yokai.
• Yingcao, trembling and terrified, manages to defeat the yokai with powerful, instinctive punches, even with her eyes closed.
• Yingcao's amulet, Tsukumo, transforms into a ghost head and devours the yokai.
• Yingcao, still frightened, asks about the yokai's disappearance.

Character Developments

• Yingcao: Yingcao demonstrates unexpected strength and courage in protecting Yōki, despite her fear. She also shows a lack of awareness or memory of her actions during her fear-induced state.
• Yōki: Yōki witnesses Yingcao's hidden power and is surprised by her actions.

Significant Themes

• Fear and Courage: Yingcao's fear is palpable, yet she acts courageously to protect Yōki.
• Hidden Strength: Yingcao's true power is revealed under extreme circumstances, suggesting that one's capabilities may extend beyond self-perceived limits.

Character Interactions

• Yingcao and Yōki: Yingcao's protective actions towards Yōki strengthen their bond, with Yōki showing concern and surprise towards Yingcao's actions.
• Yingcao and the Yokai: Yingcao's fear turns into a powerful defense against the yokai, leading to their defeat.

Key Plot Points and Events

• Yingcao effortlessly defeats four yokai, surprising Mei and Yōki.
• Mei and Yōki encourage Yingcao to believe in her strength and use it to protect her companions.

Character Developments

• Yingcao: Realizes her own power and gains confidence, deciding to protect her companions.
• Mei: Shows understanding and support for Yingcao's growth, encouraging her to believe in herself.
• Yōki: Expresses gratitude towards Yingcao and supports her, showing a gentle and generous nature.

Significant Themes

• Self-belief and confidence: Yingcao learns to trust in her own strength and power.
• Protection and companionship: Yingcao's desire to protect her friends drives her growth.

Character Interactions

• Mei and Yingcao: Mei guides and encourages Yingcao, helping her understand and accept her power.
• Yingcao and Yōki: Yōki expresses gratitude and support for Yingcao, strengthening their bond.

Key Plot Points and Events

• Yingcao expresses motivation and confidence, despite uncertainty about her words.
• Mei decides to teach Yingcao martial arts, specifically Inch Heart Fist, deeming it powerful and suitable for Yingcao's talent.
• Yōki expresses fear of Tsukumo after seeing its demon head form, but Mei assures her it's a Holy relic of the Oni Clan and has recognized Yingcao as its master.
• Yingcao notices Tsukumo's change and becomes anxious about it.

Character Developments

• Yingcao demonstrates determination and eagerness to learn.
• Mei shows consideration and willingness to help Yingcao, displaying a nurturing side.
• Yōki reveals her fearful side, showing she's not entirely fearless despite her brave front.

Significant Themes

• Mentorship and guidance: Mei considers teaching Yingcao martial arts and even taking her as a disciple.
• Transformation and acceptance: Yingcao must accept Tsukumo's true form, and Yōki must accept Tsukumo's fear-inducing appearance.

Character Interactions

• Mei and Yingcao: Mei contemplates teaching Yingcao martial arts and possibly taking her as a disciple, showing a caring and nurturing side.
• Yōki and Mei: Yōki seeks Mei's comfort and reassurance about Tsukumo, highlighting their close relationship.
• Yingcao and Tsukumo: Yingcao expresses concern for Tsukumo's changed appearance, showing her affection for the creature.

Key Plot Points and Events

• Mei and Yingcao find that Yingcao's Tsukumo has undergone significant changes: it has grown leaves resembling Yingcao's hair ornaments, its eyes have turned blood-red, and its mouth has sharp fangs.
• Mei speculates that the Tsukumo's changes might be due to Yingcao's influence as a plant yokai.
• Mei decides to help Yingcao gain confidence by having her defeat yokai.

Character Developments

• Yingcao: Shows concern for her Tsukumo and feels hesitant about defeating yokai, displaying her kind and timid nature.
• Mei: Demonstrates her protective and encouraging side towards Yingcao, showing she cares for her friend's well-being.

Significant Themes

• Friendship and Support: Mei's actions show her commitment to helping Yingcao overcome her fears and gain confidence.
• Change and Adaptation: The Tsukumo's transformation highlights the theme of change and adaptation, both in terms of physical appearance and potential abilities.

Character Interactions

• Mei and Yingcao: Their interaction shows a growing bond of friendship, with Mei acting as a supportive and protective figure towards Yingcao.
• Mei and Yōki: Though not present in this chapter, their bond is implied as Mei takes Yōki along to help Yingcao.