Eris

Biodata

Power Progression

Background

Eris first encountered Cain and the starving Ghislaine after they emerged from the wasteland into the Fittoa Region. Although initially stern and suspicious, she shared two loaves of bread when Cain explained they had not eaten for months. Cain never forgot this act of kindness. 101

After Sauros and Philip Boreas Greyrat sheltered Cain and Ghislaine, Cain became Eris's personal guard and, alongside Ghislaine, one of her swordsmanship teachers. Eris initially rejected tutoring and wanted Cain only as her guard, but changed her mind after witnessing his Fourfold Blade of Light cut through armored guards using a wooden sword. 102 103

Cain's protection of Eris was also tied to Orsted's instructions: Eris was identified as vital to bringing the Fittoa Region into Princess Ariel's future faction. Cain nevertheless treats her safety as a personal obligation, both because of Orsted's request and because she saved him. 95 158 Orsted later reassured Cain that Eris would not obstruct his plans and apologized for having tested him over the matter. 171

Cain's unexplained departure from Fittoa caused Eris to believe that he had abandoned her. She stopped eating and drinking, became catatonic, and collapsed from exhaustion before recovering when Cain returned. The incident made both of them recognize the extent of her fear of abandonment; Cain thereafter promised to tell her before leaving and not leave her behind. 159 160 166 167

Following the Teleportation Incident, Eris was displaced to the Demon Continent with Cain and Rudeus. Separated from House Boreas and uncertain whether her relatives had survived, she came to regard Cain as her remaining family and resolved to stay with him through the long journey home. 197 198

After returning to the Three Magic Nations, Eris reunited with Sauros. He told her that House Boreas and the Fittoa Region had fallen and that Philip, Hilda, and Auber remained missing. 224 Cain later found a possible lead: a new Boreas empire in the Conflict Zone has a bodyguard whose description matches Auber. He suspects its unidentified king and queen may be Philip and Hilda, but their identities have not been confirmed. 259

Appearance

Eris is a red-haired Boreas noblewoman with ruby-red eyes and a prominent cowlick. At her first meeting with Cain, she wore a delicate white dress and sunhat; she was often described standing with folded arms, legs apart, and an aggressively proud expression. 101 102

• Bright red hair, sometimes styled into twin-tails when attempting formal manners. 102 107
• Ruby-like red eyes. 101
• A distinctive red ahoge/cowlick. 101 107
• Her demeanor and fighting style increasingly resemble a beastkin warrior rather than a conventional noble lady. 133 145
• Years of sword training have turned her into a taller, physically formidable young swordswoman; by the Demon Continent journey, she has surpassed Cain in height. 187 208
• Usually carries a sword and wears practical travel clothing rather than restricting herself to aristocratic dress. 187 208
• Cut her long red hair short before leaving for the Sword Sanctum, as a sign of her resolve to grow stronger. 251

Personality

Eris begins as spoiled, stubborn, and highly resistant to reading, writing, etiquette, and teachers who cannot hold her interest. She is quick to anger, dislikes being restrained, and tries to bargain around punishments or lessons she finds boring. 102 107 127

Her strongest trait is her refusal to accept defeat. She responds to Cain's overwhelming superiority not by abandoning swordsmanship, but by declaring that she will surpass him and become the Sword God herself. This determination drives her intense training in multiple sword styles. 109 148 152

Despite her pride, Eris is compassionate and fiercely loyal. Her decision to feed strangers in need formed the basis of Cain's attachment to her, and she later vows to protect Ghislaine, Cain, and Roxy. 101 116 132 149

Eris's attachment to Cain grows into intense romantic devotion and possessiveness. She fears abandonment, seeks physical closeness with him, and privately resolves that no woman besides herself and Roxy will take him away. Cain recognizes her feelings but maintains boundaries while she is underage. 166 175 197 198 208

Although still impulsive and combative, Eris has grown more emotionally resilient and disciplined. She accepts the dangers of Cain's offensive Battle Aura because it matches her preference for decisive attacks, and she willingly sacrifices noble social obligations for training. 176 178

After coming of age, Eris openly pursues a future with Cain. She leaves for the Sword Sanctum despite her reluctance to part from him, believing she must become strong enough to stand beside and protect him. Even after losing to Timothy Breeze, she focuses on closing the gap rather than retreating from her ambition. 250 251 252 253

Abilities & Skills

Swordsmanship

Eris trains primarily in Sword God Style under Cain and Ghislaine, while Auber develops her North God Style. Her combat is forceful, fast, and instinctive rather than elegant or conventional. 132 145

• Uses both Sword God Style's direct offense and North God Style's practical, deceptive methods. 125 133 145
• Defeated Water God Style prodigy Isolte after losing her wooden sword, using punches, smoke bombs, and a rear naked choke. 136
• Can pressure stronger sparring partners with relentless full-force attacks, though this rapidly drains her stamina. 133
• Initially fractured both hands while unsuccessfully attempting Blade of Light, but eventually achieved the technique at Sword Saint rank by nearly splitting a Magic Steel Rock. 108 178
• Her refined Sword God Style, Blade of Light, thrown knives, and North God Style tactics allow her to kill groups of Demon Continent monsters in rapid succession. 187
• Ruijerd assessed her as able to challenge an ordinary Sword King even before she fully mastered the King Dragon Sword. 187
• Instantly defeated Rudeus with a wooden Blade of Light despite his new Precognition Demon Eye: he could foresee the strike but could not move fast enough to avoid it. 209
• Easily dispatched C-rank Gray Wolves without needing swordsmanship, and later killed multiple slave traders with rapid Blade of Light strikes. She also wounded North Saint Gyes with an Advanced North God Style flying-dagger technique. 210 217
• At the Sword Sanctum, knocked Gino unconscious with Blade of Light and defeated Nina in a single exchange. Against Sword Emperor Timothy Breeze, her speed and strikes threatened him, but his experience prevailed after her wooden sword broke. 253
• Trains under Sword God Gall at the Sword Sanctum, sparring with him, Timothy, Gino, and Nina to develop beyond her existing King-level strength. 252 253 254

Battle Aura Training

Cain began teaching Eris Battle Aura after she attained Advanced Swordsman rank, identifying it as a fundamental power for warriors. 147

• Her stated goal was to progress from Sword Saint through Sword King and Sword Emperor before surpassing Cain. 148
• Full-body Battle Aura coating remained beyond her at Advanced rank; it was described as a hallmark of Sword Saint rank. 148
• Cain taught her that Battle Aura is driven by desire. Eris identified her desires as defeating Cain, remaining at his side, and protecting their companions. 176
• She trained in Cain's blade-like Battle Aura, an extremely offensive form that sharpens and coats her weapon but provides comparatively little defensive protection. 175 176
• Her Battle Aura became sharp-edged enough to support Sword Saint-level Blade of Light and was later judged similar to Cain's own destructive aura. 178 187
• The aura also greatly enhances her physical strength and speed. Its limited protection against extreme temperatures remains a concern during travel. 210 237
• After witnessing Cain develop a new, mana-merging Battle Aura, Eris stayed behind to train in hopes of reproducing it; her success has not been established. 225

Magic

Cain teaches Eris basic magic in addition to swordsmanship. 105 126

• Learned the Beginner Fire Magic spell Fireball with Cain helping channel mana through her hand. 127
• Later used invisibility magic to avoid Cain after their sparring dispute. 153
• Her early magical education was hindered by her inability and unwillingness to read spell texts. 127
• Her mana reserves remain insufficient for Intermediate Fire Magic despite continued effort. Cain consequently redirected her toward practical Lower Healing and Lower Detoxification Magic for battlefield survival. 175
• Eris admires Roxy's magic and asked her to become her teacher after witnessing Flame Vortex. 167 168
• Can cast Lower Healing Magic with an incantation; she used it to restore her injured arm after her match with Timothy Breeze, surprising the Sword Sanctum's swordsmen. 253

Academic and Noble Instruction

Cain teaches Eris reading, writing, and noble etiquette in the evenings after she drives away other tutors. 133 141

• Learns etiquette quickly when Cain personally teaches her. 133
• Continues to prefer sword and magic training over academic study. 127 145
• Rudeus later becomes her household tutor for reading, writing, and arithmetic. Eris accepts the arrangement only because Cain approves it, and she continues to struggle with literacy and frequently falls asleep during lessons. 172 174
• Can read the letters Cain and Roxy send her at the Sword Sanctum, but still struggles to write a reply and asks Gino to arrange someone to help. 254
• Cannot use a map or compass reliably, though her sense of smell helped her find Gray Wolves and locate hunters who could guide her and Cain out of a forest. 210

Equipment / Items

• Wooden training sword — her usual weapon during lessons and sparring. 107 152
• Refined steel longsword — used during her Demon Continent monster training and travel. 187
• King Dragon Sword — one of the Forty-Eight Demon Swords, entrusted to Eris by Cain after Alexander submitted to him. It manipulates gravity when infused with Battle Aura and serves as her trump card, though Eris refuses to rely on it as a substitute for her own strength. She later returned it to Alexander so he could retain his combat strength while she trained without its aid. 196 207 208 230
• Ice-blue tachi — a sword she carried to the Sword Sanctum, setting it aside when Gall required wooden weapons for her match with Timothy. 251 252 253
• Smoke bombs — used as a North God Style-inspired combat tool against Isolte and Cain. 136 152
• Throwing knives — employed alongside swordsmanship and smoke bombs in combat. 177 187 She used a poisoned dagger against North Saint Gyes. 217
• Wilderness survival gear — given by Auber as a birthday gift. 134
• Lucky necklace — given by Ghislaine for her birthday. 134

Relationships

• Cain Brand — Her master, personal guard, guardian, and central emotional attachment. Eris admires his strength, repeatedly declares that she will surpass him, and wants him to remain by her side. 102 109 147 149 After being traumatized by his unannounced departure, she became deeply afraid of losing him and increasingly treats him as both her irreplaceable family and future romantic partner. Cain cares for her deeply but refuses to exploit their age difference, asking her to wait until she can make her own mature judgment. 166 197 198 208 After her fifteenth birthday, they become intimate and acknowledge a future together. Eris leaves for the Sword Sanctum to become stronger; Cain accepts her decision, misses her, and later describes her as his second wife, though their wedding ceremony remains pending. 250 251 254 255 260
• Ghislaine — Co-teacher and mentor in Sword God Style. Eris trusts her guidance but has also challenged and physically lashed out at her when resisting lessons. 102 108 Ghislaine later observes and supports Eris's Battle Aura training and continued development as a Sword Saint. 176 178 She accompanies Eris to the Sword Sanctum and promises Cain she will continue protecting her. 251 252
• Auber — North God Style instructor and sparring partner. His practical techniques broaden Eris's fighting style. 121 125 133 He and Ghislaine secretly observed Cain's specialized Battle Aura instruction out of interest in Eris's potential. 176 His whereabouts remain unconfirmed after the Teleportation Incident, although the description of a North God Style swordsman serving the new Boreas empire strongly suggests he may be there. 224 259
• Philip Boreas Greyrat — Her father. Philip employs Cain partly to secure Eris's future and protect her from political marriage. 103 104 110 As her devotion to Cain and sword training becomes unmistakable, Philip abandons plans to use her in a political marriage and accepts her chosen path. 176 He remains missing after Fittoa's fall; Cain suspects, but has not confirmed, that Philip rules the new Boreas empire in the Conflict Zone. 224 259
• Sauros Boreas Greyrat — Her grandfather and lord of the Fittoa Region. He helped shelter Cain and Ghislaine after Eris found them. 102 He reunites with Eris after the Teleportation Incident and, with the rest of their family missing, entrusts her happiness to Cain. 224
• Hilda Greyrat — Her mother, who worries for Eris when she leaves home with Cain and Ghislaine. 134 Hilda later assists Eris and remains grateful to Cain for protecting the family. 173 She remains missing after Fittoa's fall; Cain suspects she may be the unidentified queen of the new Boreas empire. 224 259
• Roxy Migurdia — Cain's fiancée and teacher. Eris promises to protect Roxy, though she is jealous of Cain's bond with her. 132 149 152 After Cain's return to Fittoa, Eris and Roxy develop an affectionate, trusting relationship through shared meals, hair styling, letters, and magic lessons; Eris is devastated when Roxy departs. 167 171 178 Roxy later welcomes Eris into the family as Cain's future second wife. The two continue to care for each other, and Roxy agrees to wait for Eris before holding a wedding with Cain. 224 225 254 260
• Rudeus Greyrat — Her literacy tutor, fellow traveler, and frequent target of her fists. Eris considers him too weak to teach her anything except academics and punishes his inappropriate behavior, but she still helps plan for his safety and joins his effort to rehabilitate the Superd Tribe's reputation. 172 173 178 202 She defeats him again even after he gains the Precognition Demon Eye, demonstrating that foreseeing her attack is not enough to evade it. 209
• Isolte Cruel — Water God Style prodigy defeated by Eris. Their first encounter establishes a possible future rivalry. 136 137 Isolte remembers Eris as a rival when they meet again at the Sword Sanctum, but Eris initially fails to recognize her. 260
• Ruijerd Superdia — Traveling companion and sparring partner on the Demon Continent. Ruijerd recognizes Eris's near-Sword King potential and continues to train with her, including in the use of the King Dragon Sword. 187 207
• Alexander Kallman — Cain's North God companion. Cain entrusted Eris with Alexander's King Dragon Sword, and Alexander came to respect her for valuing her personal ability over the weapon's power. 196 208 The sword later returned to Alexander while he undertook a separate assignment. 230
• Sword God Gall Farion — Cain's former master and Eris's instructor at the Sword Sanctum. He recognizes her ambition and blade-like Battle Aura, agrees to train her, and tests her against the Sanctum's swordsmen. Eris intends to defeat him before challenging Cain. 252 253
• Gino and Nina Breeze — Sword Sanctum trainees whom Eris defeats on arrival. Gino later helps arrange a way for her to send a written reply home; Nina, jealous and skeptical of Eris's claims about Cain, delivers Eris's message to him and discovers that their relationship is genuine. 253 254 255
• Timothy Breeze — Sword Emperor and Gino's father. His experience allows him to defeat Eris in their wooden-sword match, revealing the gap she hopes to close through training. 253
• Nanahoshi — Fellow traveler whom Eris initially misunderstands when Nanahoshi refuses a drink; Eris accepts her explanation that consuming mana-containing food or drink poses a medical risk. 220 248

Story Role / Major Arcs

Rescue in Fittoa and Becoming Cain's Disciple

Eris saves Cain and Ghislaine from starvation by sharing her food, then becomes the young noblewoman Cain is assigned to guard. Her fascination with the Blade of Light leads her to accept Cain as her teacher. 101 102 103 105

Training and the Sword God Dream

Under Cain, Ghislaine, and Auber, Eris abandons much of her former noble-lady behavior for a life centered on combat. She declares her ambition to become the Sword God and surpass Cain. 109 132 145

Water God Style Dojo

Eris accompanies Cain to the Water God Style dojo and fights Isolte in his place. Her unconventional victory humiliates the dojo's expectations of her as a sheltered noble child and earns Reida's respect. 136 137

Buena Village Training

During the group's stay in Buena Village, Eris reaches Advanced Swordsman rank and begins Battle Aura training. She continues to grow more attached to Cain, pledging to defeat him and make him stay with her. 146 147 149

The Gap with Cain

A sparring match forces Eris to confront the enormous difference between herself and Cain: he catches her full-force strike one-handed and defeats her smoke-bomb tactic immediately. Hurt but not deterred, she resolves to treat him as an enemy to overcome. 152 153

Separation Anxiety and Battle Aura Instruction

Cain's sudden departure from Fittoa leaves Eris catatonic and physically weakened by her fear that he has abandoned her. After he returns, Cain reassures her, promises better communication, and begins specialized instruction in his blade-like Battle Aura. Eris openly identifies staying with Cain and protecting their companions as central motivations for her strength. 166 167 175 176

Sword Saint Advancement

Over four further years of relentless training, Eris develops a sharp-edged Battle Aura and finally performs Blade of Light strongly enough to nearly cleave a Magic Steel Rock. Cain formally recognizes her as a Sword Saint, marking her transition from a gifted child trainee into an accomplished swordswoman. 178

Demon Continent Journey

After the Teleportation Incident, Eris travels the Demon Continent with Cain, Rudeus, Ruijerd, and later Alexander. She trains through real monster battles, reaches a level Ruijerd considers capable of facing an ordinary Sword King, and becomes increasingly inseparable from Cain as both a companion and chosen family. 187 197 198 202

King Dragon Sword

Cain gives Eris the King Dragon Sword after accepting Alexander as a companion. Though she initially struggles with the massive weapon, she learns to use its gravity manipulation to bring her Sword God Style to approximately King-class strength. She nevertheless insists on treating the sword as a reserve weapon rather than relying on its power for her identity as a swordswoman. 196 207 208 She later returns it to Alexander so that he can use it on his own assignment while she trains without depending on it. 230

Ent Port and Her Future with Cain

At Ent Port, Eris's growing strength earns praise from Ruijerd and Alexander. During a shopping trip, she presses Cain about their future relationship; Cain refuses her advances while she is underage but admits his affection and promises not to change his mind once she is old enough to choose for herself. 207 208

Adventuring and the Beastfolk Rescue

Eris defeats Rudeus in a spar even though his new Precognition Demon Eye lets him see her attack coming. She then persuades Cain to take a Gray Wolf extermination quest with her. Their fighting easily completes the quest, but neither can navigate the forest by map; Eris finds the wolves and later some helpful hunters by smell. 209 210 During a later rescue of imprisoned Beastfolk girls, Eris fights the slave traders, rapidly killing several and wounding their leader, North Saint Gyes. 215 217

Return and Reunion with Sauros

Eris travels with Cain, Ruijerd, and Nanahoshi toward the Ancient Teleportation Array Ruins, declaring that wherever Cain is feels like home. 220 After returning to the Three Magic Nations, she reunites with Roxy and Sauros. She learns that Fittoa has fallen and her parents remain missing; Roxy welcomes her as part of the family, and Eris joins her in reassuring Cain that he need not bear every danger alone. 223 224

Coming of Age and Departure for the Sword Sanctum

At her fifteenth-birthday celebration, Eris takes the initiative in expressing her desire for a relationship with Cain. Afterward, she cuts her hair short and leaves a letter explaining that she is going to become stronger because she does not yet feel worthy of standing beside him. Ghislaine accompanies her to the Sword Sanctum. 250 251

Sword Sanctum Training

At the Sanctum, Eris defends Cain against disciples who mock him. Gall reveals that Cain had defeated him years earlier and agrees to train Eris after hearing her goal of surpassing and protecting Cain. 252 Eris defeats Gino and Nina, then challenges Sword Emperor Timothy Breeze. Her speed and Blade of Light threaten him, but his experience wins their match. She heals her injured arm with magic and begins intensive training with Gall and the other swordsmen. 253 254

Cain and Roxy send Eris weekly letters. Unable to write back easily, she arranges help through Gino and asks Nina to tell them she loves them, plans to return after defeating Gall, and wants a wedding ceremony. Nina visits their villa expecting to expose a lie, but Cain and Roxy confirm their love for Eris. 254 255 Gall later summons Water God Reida to assist Eris's training, bringing Eris face to face with her former opponent Isolte. 260

Notable Quotes

“I'm going to become the Sword God!” 109

“Once I defeat Master Cain, I'll go ask Master's master. Just like Cain protected me, I'll protect Master Cain too! And Master's master Roxy!” 149

“I want to defeat Master Cain! And make Cain stay by my side forever.” 176

“I want to surpass Master Cain... and protect him by his side!” 252