Gu Yu

Biodata

Feature	Information
Name	Gu Yu (古雨)
Alias(es)	Kamen Rider Decade; Dark Decade (Terra incident) 552
Species/Race	Human; his past includes modification and brainwashing by an unnamed organization 311
Gender	Male
Affiliation	St. Freya Academy’s dormitory group; ally of Schicksal and Anti-Entropy personnel
Occupation/Role	Protagonist; former mercenary who investigated his Stigmata while aiding orphanages 762
Status	Alive; returned after being believed dead or missing following the final battle 761 774
Birthdate	January 11, 2000 36
First Appearance	Chapter 1, “Thanks for the Invite... I’ll Thank Your Head!”

Power Progression

Stage / Realm / Level	Chapter	Notes
Decade Rider system awakened	1 2	Arrives in Changkong City with Honkai knowledge and transforms through the Rider Emblem; first shown changing into Kuuga Dragon Form and wielding the Azure Dragon Staff.
Honkai Energy Absorption and Aurora Curtain	69	The man in black transfers both abilities to him, granting energy absorption and dimensional traversal.
Belt Mimicry and Sound Blade Armor	208	Mimics the Decade Driver, transforms the Key of Domination into the Sound Strike Amplifying Sword, and manifests Sound Blade Armor.
Ultimate Kuuga and Blade King Form	243	Learns that forms can be unlocked by fulfilling conditions rather than only absorbing Honkai Energy; King Form permits direct use of Undead abilities without card swipes.
Build Genius Form	332	Applies two Pseudo-Herrscher Cores and Belt Mimicry to manifest Build Genius Form and its sixty Full Bottle abilities.
Herrscher authority absorption	749 750 752	Becomes a Herrscher, absorbs the authorities of Rock, Flame, Binding, Corrosion, and other defeated Herrschers while defeating their coalition.

Background

Gu Yu’s physical body entered the Honkai world in 1995, but a problem with that body caused his soul to attach to an infant with the same name. His parents were killed by Sirin during the Second Honkai War in 2000; afterward, greedy relatives ransacked his home, and he fled rather than fight adults for it. 762

He later became a mercenary, researching the Stigmata on his hand and helping orphanages where he could. In February 2014, he traveled to Changkong City for a mission. The Third Honkai Outbreak occurred a month early, and his awakening of Decade’s power coincided with monsters from other worlds beginning to transmigrate there. 762

At the beginning of the novel, Gu Yu awakens in Changkong City with memories and lore from Honkai Impact 3rd. Recognizing the city and the impending outbreak, he immediately prioritizes survival and escape. 1 His knowledge of events gives him a major tactical advantage, though he conceals that knowledge from his companions. 186

Appearance

Gu Yu’s untransformed design centers on a wry smile, a black vest, and a white outer coat. The contrast is intended to represent his outwardly “pure white” image and the “pitch-black person” residing within him. 779

• Black vest beneath a white outer coat. 779
• Often wears full-body Kamen Rider armor in combat, leading others to mistake him for a monster. 100
• Uses a Decade Driver and Card Holder at his waist while transformed. 612

Personality

Gu Yu is reserved, wary of intimacy, and slow to become familiar with others, particularly girls. Despite initially appearing blunt and straightforward, he is described as a shut-in who constantly overthinks when he is not fighting. 26 123 He maintains emotional distance even from people he protects, partly due to his missing memories and unresolved past. 182 344

In battle, he is decisive, sarcastic, and often ruthless toward active threats. He analyzes enemy abilities, improvises counters, and is willing to take damage to create an opening. 270 458 Outside battle, he consistently protects civilians, heals injured allies and former enemies, and refuses to abandon people even when doing so would be safer. 106 181 718

His greatest flaw is self-neglect. Gu Yu repeatedly fights while exhausted, injured, or suffering Honkai Energy erosion, believing he must handle dangers himself before they harm others. 265 450 649

Abilities & Skills

Kamen Rider Transformations

Gu Yu uses the Decade system to access a large range of Kamen Rider forms, armors, weapons, and finishing moves. Kevin estimates that Gu Yu possesses at least twenty distinct combat armors, with the true number potentially much higher. 615

• Changes forms through Form Ride and Kamen Ride cards, adapting to an enemy’s element, range, speed, or defenses. 174 198
• Mimics Riders’ belts to gain a form’s inherent capabilities, including special armor and weapon effects. 208 243
• Uses forms including Kuuga, Kiva, Blade, Agito, Hibiki, Build, Gaim, Ghost, OOO, Ryuki, and Dark Kiva. 2 68 208 243 332 514 552 703
• Rapid form-switching can heavily burden his body, especially when using powerful forms or mimicked belts. 208 704

Rider Cards and Manifested Armaments

His Card Holder stores Ride cards, Undead cards, sealed souls, and abilities. He can manifest weapons or combine card effects to create layered attacks.

• Enhances Wake Gun shots with Undead cards for greater power and rate of fire, then uses homing attacks against evading targets. 25
• Uses Attack Ride and Final Attack Ride cards for mobility, barriers, invisibility, elemental attacks, weapon summoning, and finishing moves. 48 443 750
• Can seal souls in cards, including Yae Rin and Dan Zhu, in order to preserve or later release them. 36 201
• His Driver, Card Holder, and right-hand Stigmata are recognized weaknesses; damaging either can disrupt his combat ability. 612 750

Honkai Energy Absorption and Herrscher Authority

Gu Yu can absorb Honkai Energy and later acquires the authorities of defeated Herrschers. 69 749 750

• Absorbs Honkai Energy after defeating enemies and draws in special energies compatible with his Rider powers. 7 678
• Absorbs Herrscher authorities after defeating their holders, including Rock, Flame, Binding, and Corrosion. 749 750
• His absorption ability may protect him from some Herrscher authorities, but it also contributes to dangerous Honkai Energy erosion. 646 649
• Excessive absorbed energy and repeated transformation strain his body and mind, leaving him vulnerable to collapse or loss of control. 538 704 754

Aurora Curtain

The Aurora Curtain is Gu Yu’s dimensional movement and spatial-control ability, obtained from the man in black. 69

• Opens rifts for rapid travel across vast distances, including a trip from the Far East to ROS in under twelve hours. 107
• Creates barriers and enclosed spaces for combat, concealment, and protection. 102 121
• Can be used tactically to bind or reposition opponents. 458
• Has significant limitations despite its utility, as warned by the man in black. 69

Regeneration and Molecular Manipulation

Gu Yu can repair physical damage through molecular manipulation as long as he is not killed instantly. 2

• Regenerates severe injuries, including a severed arm during his battle with Kevin. 375
• Uses restorative cards to heal allies such as Fu Hua, Lin, Su, and wounded civilians. 106 286 313
• Recovery does not eliminate mental exhaustion, Honkai erosion, or the bodily cost of prolonged transformations. 538 649 704

Combat Analysis

Gu Yu’s main strength is not only his arsenal but his ability to read opponents and build counters during battle.

• Predicts movements through abilities such as Musashi Soul, True Eye, and enhanced perception forms. 132 533
• Analyzes enemy data through weapons such as the Dogga Heavy Hammer and specialized forms. 241 678
• Uses traps, feints, reflected attacks, and deliberate injuries to create decisive openings. 48 270 458
• Acknowledges that his raw combat skill can be inferior to experienced fighters such as Kevin, forcing him to rely on deception and adaptability. 375

Equipment / Weapons / Items

• Decade Driver — Primary transformation belt and card reader; can be mimicked or altered for higher forms. 208 243
• Card Holder / Card Holder Sword — Stores and deploys Rider, Attack Ride, Final Attack Ride, and sealed-soul cards. 25 201
• Rider Cards — The source of Gu Yu’s transformations, attacks, finishers, and borrowed abilities. 48 443
• Key of Domination / Sound Blade Armor — A transformed weapon used with Hibiki Kurenai and Shikigami armor. 208
• Dogga Heavy Hammer — Analyzes enemies and uses True Eye to immobilize them. 241 678
• Ultimate Titan Sword, Azure Dragon Staff, and Pegasus Bow — Weapons used with Seal Energy against the Herrscher of Thunder. 198

Relationships

• Raiden Mei — Initially meets Gu Yu during the Changkong City outbreak. He repeatedly protects her from the Herrscher of Thunder and later heals her after subduing that persona. Gu Yu is later stated to like Mei. 1 628 774
• Kiana Kaslana — Companion whom Gu Yu protects from Honkai threats and from the trauma of seeing Cecilia controlled as an undead. Kiana jokingly introduces herself as his fiancée, which he immediately rejects. 241 259
• Bronya Zaychik — Trusted companion and information source. Gu Yu relies on her hacking and privately asks her to investigate Fu Hua’s movements; he also advises her not to blame herself for Cocolia’s actions. 96 119
• Yae Sakura — Former opponent whom Gu Yu helps free from Hiyorimar’s influence. Sakura later calls him her savior and expresses unwavering devotion to him. 30 227
• Azuma Yuno — Former enemy who becomes a companion. She openly criticizes Gu Yu’s habit of charging into danger and remains attentive to his worsening erosion. 186 649
• Fu Hua — Begins as an adversary under Otto’s influence. Gu Yu defeats and heals her rather than killing her; afterward, the two develop a wary but mutual concern. 106 450
• Rita Rossweisse — A teasing, provocative acquaintance who later becomes one of Gu Yu’s closest companions. Bishop identifies Rita as the person Gu Yu cherishes most. 107 679
• The Man in Black / Dark Decade — Gu Yu’s identical-looking counterpart and recurring rival. He grants Gu Yu Honkai Energy Absorption and Aurora Curtain, then repeatedly tests him in increasingly dangerous battles. 48 69 722
• Chen Tianwu — A man Gu Yu saves alongside his sister, Chen Tianwen. Chen later risks his life to transmit intelligence about the Honkai Energy Fission Bomb to Gu Yu. 538 718
• Lin Ran — Gu Yu’s old acquaintance who saves him after his death and assigns him to help prevent destructive Ohma Power users from harming other worlds. 761

Story Role / Major Arcs

• Changkong City Outbreak — Awakens in 2014, realizes the Third Honkai Outbreak is imminent, and fights alongside Raiden Mei and Kiana. 1 7
• Dark Decade Conflict — Encounters a black-armored counterpart with the same appearance and Rider abilities; their rivalry becomes central to Gu Yu’s growth. 48 68 69
• ROS and St. Freya Missions — Opposes Cocolia’s plans, confronts Siegfried and Fu Hua, protects Lin, and becomes a key member of the St. Freya group. 96 106 119
• Chi You and Ancient Souls — Battles the Herrscher of Thunder, enters the Chi You conflict, rescues Dan Zhu and Cang Xuan, and unlocks Blade King Form. 198 201 243
• Global Anti-Honkai Battles — Fights Gurongi, Herrschers, World Serpent forces, and other cross-world threats while his physical condition worsens. 286 375 538 649
• Terra Excursion — Awakens with recovered memories in Chernobog, destroys Reunion’s immediate threat, frees Talulah from Koschei, and coerces Ursus leaders into acting on intelligence against a coming war. 552 553
• Fangire War — Investigates Fangire infiltration, protects Rita from Bishop’s scheme, and battles King using Dark Kiva and Emperor Power. 670 679 703 704
• Final Herrscher Battle — Becomes a Herrscher, absorbs multiple authorities, and fights the Honkai God’s forces despite near-fatal erosion. 749 750 754
• Aftermath and New Mission — Disappears after transforming into light, later returns through Lin Ran’s intervention and accepts a mission to stop destructive Ohma Power users from harming other worlds. 761

Notable Quotes

“Sorry... I can still fight!” 2

“Miracles and magic are not free.” 36

“Who told you I was planning to leave?” 241

“Is all of this worth it?” 302

Trivia

• Gu Yu is an only child; his name does not come from the “Guyu” solar term and he has no sister named Lixia. 36
• The name was formed from “Gu” and “Yu,” reflecting the author’s hope that he would overcome laziness and desire to become a writer. 36
• He has a local identity in Changkong City despite the unusual circumstances of his transmigration. 60
• Gu Yu’s white-and-black clothing motif deliberately mirrors the man in black: Gu Yu appears white outside while concealing darkness within, whereas the man in black has a dark exterior and an initially pure interior. 779