Little White Mouse

Biodata

Feature	Value
Name	Xiao You; named by Yui Hyuga 32
Alias(es)	Little White Mouse (小白鼠); rejects “Little White” as a proposed name 22
Species/Race	White laboratory mouse turned summoning beast; exact awakened bloodline unidentified 18 22 24 32
Gender	Female 22 37
Affiliation	Yui Hyuga, through a bloodline contract 22 28
Occupation/Role	Former experimental subject; Yui’s summon, companion, and sealing-jutsu specialist 18 23 32
Status	Alive; accompanying Yui in Shikkotsu Forest 37 40
First Appearance	Chapter 18, as the mouse bearing an experimentally applied Caged Bird Seal 18

Power Progression

Stage / Realm / Level	Chapter	Notes
Awakening of intelligence and memories	22	After Yui’s deathlike-state experiment, unfamiliar memories appear in her mind, enabling thought and human speech. She also survives beyond the blood-transfusion procedure’s expected two-day limit.
Bloodline contract with Yui	22 28	Consumes one drop of the original Yui’s blood and glows gold as the bond forms. Its nature is later identified as a bloodline contract.
Golden sealing technique demonstrated	23	Uses knowledge from her awakened memories to temporarily open a communication vortex through Yui’s confinement seal; cannot remove the barrier outright.
Summoning compatibility confirmed	28	Yui successfully summons her from a cage through their existing bloodline contract, without forming a separate summoning contract.
Summoning Technique learned	29	Learns the technique after three days of training. Summoning Yui requires additional chakra and a drop of Yui’s blood.
Contract Seal broken	32	Channels golden chakra to destroy Ikuko Hyuga’s Contract Seal, allowing Yui’s summons to retrieve her.

Background / History

Laboratory Origins

Xiao You originated among the white mice Yui specially bred for biomedical experiments. These mice normally lived for less than a year and had genes described as ninety percent similar to those of humans. Yui transfused her own blood into this particular mouse through the Blood Exchange Technique, fooling the Caged Bird Seal’s bloodline detection and allowing it to be applied. The transfusion was expected to leave the mouse alive for only two days 18.

Yui subsequently induced a deathlike state with a drug, causing the Caged Bird Seal to register brain death and disappear. An electric shock reactivated the mouse’s brain, and she awakened successfully. Yui kept her for observation because she had survived numerous experiments and appeared unusually intelligent 19.

Three days later, Yui’s laboratory Shadow Clone discovered that the mouse could speak. The mouse attributed her new intelligence to memories that appeared after she was knocked unconscious, but could not verbally disclose their contents. Grateful to Yui for what she considered a second life, she accepted a bloodline contract and accompanied the clone to investigate the original Yui’s absence 22.

Attempts to Free Yui

At Yui’s sealed room, Xiao You identified the confinement barrier and temporarily opened a vortex through which the original and clone could communicate. The effort exhausted her, leaving her severely emaciated. Yui supplied chakra, restoring some of her weight, before she fell asleep for several days 23 24 26 28.

After awakening, she learned the Summoning Technique to help retrieve Yui’s imprisoned body. When Ikuko intercepted the clone, Yui sent Xiao You away to obtain blood and find Yamada Hideko. A locked laboratory door prevented her from collecting the blood, and her attempts to ask passersby for Hideko’s whereabouts caused a public disturbance 28 29 31.

The Military Police detained her, and Captain Chengdou suspected she might be a foreign spy’s summon. Ikuko identified her as Yui’s summoning beast, then captured her and applied a Contract Seal. Xiao You mentally called for Yui, broke the seal with golden chakra, and escaped through Yui’s summons. Once reunited, Yui named her Xiao You and declared that they were family rather than master and servant 32.

Separation and Reunion

Yui’s experimental escape through the Summoning Technique left Xiao You behind in the sealed room. Spatial turbulence displaced Yui by roughly a year, during which Xiao You remained confined, spending her days eating and sleeping 33 35 37.

Yui eventually summoned her to Shikkotsu Forest and explained the unintended separation. Xiao You’s distress subsided, and she immediately asked whether Yui had been hurt. She then met Katsuyu, who welcomed her as a companion 37.

Appearance

• White fur and jet-black eyes: Her ordinary appearance contrasts with the golden light produced by her sealing power 23.
• Fluffy tail: Yui finds this especially appealing; Ikuko later recognizes it as a clue that she is not an ordinary mouse 22 30 31.
• Tiny body and short legs: Small enough to ride on Yui’s shoulder or sleep in her pocket 24 33.
• Golden markings: When using her barrier technique, luminous patterns spread across her fur and her eyes shine gold 23.
• Former forehead seal: Initially bears a blue-green Caged Bird Seal, which disappears after Yui’s successful experiment 18 19.

Personality

Xiao You is grateful and deeply attached to Yui. She accepts their initial master–servant bond because she believes Yui gave her a second life, volunteers to learn summoning without hesitation, and blames herself when the rescue plan fails. Yui’s decision to treat her as family gives her a more personal sense of belonging 22 28 32.

She is proud of her inherited sealing knowledge but easily discouraged by her limited strength. Affection embarrasses her, while perceived abandonment causes considerable distress. She also dislikes being handled roughly and becomes distraught when a police officer steps on and dirties her fluffy tail 22 23 28 31 37.

Abilities & Skills

Awakened Memories and Speech

Her unexplained memories provide both human speech and specialized knowledge 22 23.

• Can converse with humans and other summoning creatures 22 37.
• Cannot directly recount the memories’ contents: attempts produce squeaks instead of intelligible speech 22.
• Yui suspects inherited memories and an ancient bloodline, but Xiao You’s exact nature remains unidentified 22 24 37.

Sealing Jutsu

Xiao You understands sealing mechanisms beyond her current ability to dismantle them 23.

• Identifies Yui’s barrier as an intermediate chakra-absorbing seal with primary and secondary points 23.
• Explains that attacks strengthen the barrier and excess absorbed energy is redirected to its secondary point 23.
• Opens a temporary communication vortex for at most fifteen minutes, rather than fully removing the barrier 23.
• Suffers severe exhaustion and weight loss after sustaining the vortex; requires chakra and prolonged sleep to recover 24 26 28.
• Can break Ikuko’s Contract Seal with golden chakra, despite being unable to undo the confinement barrier 23 32.

Bloodline Contract and Mental Contact

Her bond with Yui is a bloodline contract rather than an ordinary summoning contract 28.

• Formed by consuming one drop of the original Yui’s blood 22.
• Supports Yui’s use of the Summoning Technique to retrieve her 28 32 37.
• Allows her mental cry for help to reach Yui 32.
• Enables her to sense Yui’s presence; she notices that connection disappear during Yui’s induced deathlike state 40.

Summoning Technique

Yui teaches Xiao You the hand seals boar, dog, bird, monkey, ram to prepare for rescuing her original body 28.

• Learns to use the technique within three days 29.
• Lacks sufficient chakra for the intended rescue without Yui’s assistance 29.
• Requires Yui’s blood to summon her because Yui is the master in their bloodline contract 29.

Relationships

• Yui Hyuga — Breeder, former experimenter, contracted partner, and chosen family. Yui names her Xiao You because the name sounds like the first syllable of her own, and asks her to stop calling her “Master” 18 22 32.
• Yui’s Shadow Clone — Discovers her speech, forms the initial contract using the original’s stored blood, and teaches her summoning 22 28.
• Ikuko Hyuga — Pursuer and captor. Tracks her footprints with the Byakugan, but refrains from killing her because Yui would blame her 31 32.
• Yamada Hideko — Intended source of rescue assistance; Xiao You searches for her on Yui’s instructions but does not reach her 29 31.
• Katsuyu — Fellow companion of Yui. Welcomes Xiao You warmly, then startles her by revealing a slug-like form beneath her human transformation 37.

Notable Quotes

“You awakened my memories. That's as good as giving me a second life.” 22

“Waaah, Yui, I thought you'd abandoned me!” 37