Bai Yu

Biodata

Power Progression

Bai Yu’s system measures physical attributes rather than named realms. Its reference values place an ordinary person around 50 and trained individuals around 65–75; reaction speed is described as largely innate and difficult to improve 4.

Background / History

In his previous life, Bai Yu attended a Project 211 university and became an overworked employee. Anime was one of his few pleasures. Despite medical tests revealing poor health, he continued working and died during several days of overtime. He then awoke in his new world as a baby, retaining his memories and receiving a training-oriented system 1 36.

An elderly couple adopted and raised him alongside Xiate, called Hiette Doyle in the opening chapter. Their grandfather died in 843, following their grandmother; the family’s biological son had belonged to the Survey Corps and had only an empty grave. Bai Yu and Xiate subsequently relied on each other and worked at a restaurant under Sister Shi 1 2 4.

By 844, Bai Yu recognized his surroundings as the world of Attack on Titan and knew that Shiganshina would fall in 845. He scanned the district into his virtual training ground and repeatedly practiced surviving Titan invasions. Although he initially claimed that he could not protect everyone, he prepared to save people close to him when the breach approached 1 3 5 6.

Appearance

Bai Yu initially appears as a boy barely into his teens, approximately one and a half meters tall, although he identifies himself as ten when joining the Survey Corps 1 12.

• Hair: Fairly short 3.
• Eyes: Described as having a silvery sheen, with a faint red glow during his threat to Erwin 10.
• Usual expression: Sleepy, languid, or apparently unfocused, even before combat 1 3 15.
• Military clothing: Survey Corps cloak bearing the Wings of Freedom and, later, customized mobility gear 15 24.
• Battlefield appearance: After killing twenty-five Titans, his blood-soaked clothes and rising steam prompted comparisons to an asura 17.

Personality

Bai Yu is easygoing, mischievous, and openly fond of sleeping. He teases Xiate, jokes about Levi’s height, and is content to let other soldiers underestimate him if they leave his naps undisturbed. Much of that apparent idleness conceals training or research conducted while his body sleeps 4 12 13 36.

His casual manner coexists with extraordinary persistence. Repeated virtual deaths, severe pain, and mental exhaustion do not stop him from training. He explains that even a slight desire to accomplish something can sustain his effort indefinitely. In Paths, however, he admits that his pleasures and motivations are difficult to describe and welcomes a rare opportunity to rest without training 3 4 39 40.

Protecting his inner circle takes priority over abstract heroism. He insists that Ming and Xiate learn to kill human enemies without hesitation and rejects the idea of them sacrificing themselves for strangers. His threat to Erwin over Xiate’s safety exposes how ruthless he can become when someone important to him is endangered 10 25.

As an instructor, Bai Yu becomes strict and sometimes physically brutal. Outside training, he shares meals, expedition stories, and jokes with the cadets, who come to regard him as both a senior and a friend. He openly says that harsher training reflects greater affection, with Kali receiving particularly demanding instruction 29 37.

Abilities & Skills

System Training Ground

The system provides a configurable virtual environment in which Bai Yu trains and experiments. It evaluates physical improvements made there and transfers them to his real body 1.

• Environmental scanning: Objects and terrain scanned in reality can be reproduced, including Shiganshina and sections of Wall Rose 1 12.
• Time advantage: The initial time-flow ratio is two to one; the system says this can change with mental strength 1.
• Daily allowance: Ten hours of training time, supplemented by quest rewards; unused time can be saved for later 1 25.
• Optional quests: Meals, work attendance, and sleep award training time, books, or items without penalties for failure 4.
• Reset function: Restores his virtual body and the training environment after he loses consciousness; it also makes dangerous experiments survivable within the simulation 3 36.
• Limits: Knowledge must be learned from books rather than downloaded directly. Training still causes pain and mental fatigue 1 4.

Omni-Directional Mobility Gear Combat

Bai Yu combines precise gas control, aerial movement, blade throws, and rapid nape attacks. Erwin’s observers describe his recruitment demonstration as the pinnacle of mobility-gear maneuvering 10.

• Kills fifteen-, seven-, and ten-meter Titans in one ten-second sequence without firing grappling hooks, then kills a distant five-meter Titan with thrown blades 10.
• Uses a thrown blade to cripple a Titan before finishing it and cushioning his return to horseback with gas 15.
• Kills twenty-five Titans single-handedly during an expedition while rescuing soldiers 17.
• Serves as the Support Squad’s main attacker while Ming and Xiate disable limbs and create openings 17 21 22.
• Remains limited by stamina, gas, blades, and available terrain. Multiple Titans on open ground are substantially more dangerous than urban engagements 8 13.

Hand-to-Hand and Armed Combat

Bai Yu prepares for human opponents as well as Titans, using simulated enemies modeled on himself 3 28.

• Progresses from defeating two fixed copies of himself to defeating three updated copies after more than a year; four armed copies remain beyond him 28.
• Defeats the assembled cadets, including Eren and Mikasa, during his instructional demonstrations 27 28.
• Dislocates and resets Annie’s arm when she challenges him 29.
• Teaches horse stances, posture, sparring, and joint attacks during a two-month combat course 28 37.

Firearms

Bai Yu practices marksmanship and armed combat in the training ground, then teaches those skills to his squad 4 25.

• Shoots a tossed stone out of the air as a demonstration 25.
• Trains Ming, Xiate, and Kali in firearm use; Ming and Xiate also receive firearm-assembly instruction 25 49.
• Fits handguns into accessible holsters on modified mobility gear as preparation for situations involving human enemies 24 25.

Forging and Weapons Engineering

Bai Yu studies system-provided manuals and uses virtual experiments to turn technical knowledge into practical equipment 8 36.

• Mobility-gear upgrades: Adds assistive exoskeleton joints, improved controls, adjusted weight-bearing points, and gas canisters with approximately 50% more capacity 12 24.
• Personal fitting: Tunes Ming’s and Xiate’s gear to their musculature and movement habits. His own highly sensitive model would be dangerous for other users 24.
• Wider production: Supplies Erwin with blueprints for a less finely tuned version; the Survey Corps later receives discreet upgrades designed to resemble its old equipment 24 49.
• Explosive weapons: Pursues Thunder Spears against the Armored Titan’s defenses and develops the Little Fish rocket 31 46 47.

Prior Knowledge and Field Coordination

Bai Yu remembers the original story and an Attack on Titan game, but recognizes that his actions have changed events and that some people do not match his expectations 1 13 14 25.

• Anticipates Shiganshina’s fall and the refugee food crisis 5 8.
• Recognizes Reiner, Annie, Bertholdt, and Ymir among the recruits 18.
• Gives Erwin leads concerning Titans’ human origins and Doctor Jaeger’s possible arrival from outside the Walls 31.
• Uses smoke signals and Ming’s danger warnings to redirect the scouting formation 22.
• Leaves political planning to Erwin while supplying information intended to prevent decisions based on faulty intelligence 36.

Equipment / Weapons / Items

• Customized mobility gear and blades — His personal equipment includes exoskeleton assistance and unusually sensitive controls; he also constructs tailored sets for his squad 12 24.
• Handgun — Carried in a holster integrated into his mobility gear 24.
• Wireless earphones — System reward with unlimited battery life, selectable or random music, and track storage. Music helps him focus in battle; one earbud remains with Ymir in Paths, playing his recorded stories 1 3 13 40.
• Technical books — Include forging and firearm manuals, physics texts, and basic and advanced missile theory. They underpin his equipment development 4 8 36 37.
• Grisha Yeager’s three books — Entrusted to him by Erwin as protection against possible memory erasure; he later presents them to Pixis 35 37.
• Little Fish — Experimental arm-mountable rocket and lightweight launcher developed with Xiate and Ming 46 47.
  • Its first successful test produces a crater roughly three to four meters across and destroys the target completely 47.
  • Bai Yu judges its blast slightly stronger than a Thunder Spear’s 47.
  • He estimates that properly trained thirteen- or fourteen-year-olds could fire it; airborne use requires additional practice 47.
  • Titan hardening may protect against it, while an unprotected blast could kill the human inside and prevent capture 47.

Relationships

• Xiate / Hiette Doyle — Adopted younger sister and Support Squad member. They vow to remain together despite danger or death; he makes her safety a condition of his cooperation with Erwin and personally trains her 1 5 10 17.
• Ming — Squad member, trusted companion, and regular drinking partner. Bai Yu values his quiet persistence and danger-sensing intuition; Ming cares for him when he becomes drunk 14 16 19 22 42.
• Erwin Smith — Commander and strategic partner. Erwin pressures him into the Survey Corps but also grants him unusual freedom, supports his recruitment requests, and provides facilities for his inventions 9 11 24 36 46.
• Levi Ackerman — Fellow elite soldier. Their early interactions include Bai Yu’s height joke and Levi’s furious response, but Levi accompanies his first expedition out of concern and acknowledges his skill 12 15.
• Yishi — Older friend who cared for the siblings after their grandfather’s death. Bai Yu rescues her, visits her after her trauma, and supports her entry into training, but considers her unready for the Support Squad 7 19 20 24 44.
• Kali Lang — Prospective Support Squad recruit and personal trainee. Her resemblance to a game’s nameless warrior motivates his interest; he supervises her dangerous practice and protects her when necessary 25 26 30 49 50.
• Eren Yeager, Mikasa Ackerman, and Armin Arlert — Childhood friends who frequently ask him about the outside world. He has repeatedly driven away Armin’s bullies and later becomes their combat instructor 2 25 28.
• Grisha Yeager — Doctor whose assistance to Bai Yu’s family helped establish their friendship with the Yeagers 2.
• Keith Shadis — Training Corps instructor who assists with Bai Yu’s recruitment and teaching arrangements; regards him as someone who would not gamble with soldiers’ lives 25 27.
• Ymir in Paths — Ancient Titan-maker whom he calls “Granny” or “Ancestor.” He keeps her company with stories and leaves her an earbud containing his voice; he does not understand how he entered or left Paths 38 39 40.
• Dot Pixis — Garrison commander to whom Bai Yu delivers the books revealing the outside world 37.

Story Role / Major Arcs

Fall of Shiganshina and Enlistment

• Prepares stolen Garrison mobility gear before the 845 breach and sets out with Xiate to save people, first approaching the Yeager home 5 6.
• Escapes aboard a refugee boat with Yishi, witnesses the Armored Titan breach Wall Maria, and discards the stolen gear to conceal his involvement 7 8.
• Initially plans to join the Garrison, but Erwin confronts him with recovered gear parts and tests his combat ability 8 9 10.
• Accepts Survey Corps service after negotiating protection for his companions and arrangements for Xiate’s early training 10 11.

Establishment of the Support Squad

• Joins the twenty-seventh expedition as the vanguard, accompanied by Levi 15.
• Earns the Sleep-Deprived Reaper nickname after an expedition in which he kills twenty-five Titans and saves soldiers, overturning doubts about his age 17.
• Obtains custody of Ming’s and Xiate’s advanced training and forms a roaming rescue unit with himself as its main attacker. The squad saves nearly a third of the Survey Corps from Titans 17.
• Secures a former warehouse as the squad’s base after offering—and fulfilling—payment of roughly one hundred Titan kills 41.

Training the 104th Cadets

• Recruits Kali and takes charge of a two-month hand-to-hand combat course 25 26 27.
• Enforces formation discipline during a sudden Titan attack; afterward, Kali agrees to join the Support Squad 29 30.
• Finishes the course with Annie first, Mikasa second, and Eren third in its combat rankings 37.

Outside-World Discovery and Government Opposition

• Reads the recovered books with Erwin and Levi, learning about humanity beyond the Walls, the Nine Titans, and Grisha’s past 34.
• Supports Erwin’s plans against the royal government and receives custody of the books as a safeguard against memory manipulation 35.
• Helps share the discovery with Pixis while advancing the Survey Corps’ weapons research 36 37.

Paths and Weapons Development

• Unexpectedly enters Paths despite possessing neither the Founder’s power nor royal blood. He spends an indeterminate period telling Ymir stories before returning just as unexpectedly 38 39 40.
• Develops and successfully tests Little Fish, recording its results and operating instructions for Erwin 46 47.
• Gives Kali intensive training followed by supervised live combat; she kills ten Titans before exhaustion, exceeding his expectation of eight 49 50.

Notable Quotes

“No matter what I do, I'll always keep you by my side.” 5

“If anything happens to her, I'll slaughter every last human above the rank of commoner.” 10

“Today's training is to kill as many Titans as there are! Kali, give it everything you've got, and don't die!” 50

Trivia

• The Sleep-Deprived Reaper nickname initially leaves him mortified, but it eventually becomes an officially recorded title 17 24.
• He considers naming Little Fish “Bai Yu,” then abandons the idea because soldiers shouting “Quick, bring out Bai Yu!” would sound strange 47.
• Although he regularly supplies Ming with liquor, his own tolerance is poor enough that Ming buys cider specifically for him 40 41 42.