You Know Who

Biodata

Feature	Information
Name	You Know Who
Alias(es)	Mysterious Person; Tom
Species/Race	Formerly human; later states that he is no longer human
Gender	Male
Affiliation	Jujutsu Society
Occupation/Role	High-school student; anonymous diarist; supernatural investigator
Status	Active
First Appearance	Chapter 1 1

Power Progression

Stage / Realm / Level	Chapter	Notes
Pure Yang Body	2	Obtains a physique that repels evil spirits, but raises his body temperature and can make him hot-headed. 2
Ripple Chi Kung	4	Gains Ripple Chi Kung; its compatibility with the Pure Yang Body lets him regulate its excess power and accelerate plant growth. 4
Yellow Temperance	17	Acquires the Stand Yellow Temperance, gaining organic-matter assimilation, bodily disguise, and voice alteration. 17
Destiny / Card Master awakening	113	Awakens power connected to space and destiny, including fate perception and teleportation; his eyes shine gold when it is used openly. 113
Grade 1 combat potential	153	His unrevealed Projection Magic, Sun Breathing, and physical ability are assessed as sufficient for Grade 1 combat power. 153
Special Grade combat power	166	With Unlimited Blade Works, the Dragonslaying Holy Sword, Pure Yang Body, and teleportation, he judges himself capable of confronting ordinary Special Grades. 166
Yellow Temperance: Wonder of U	182	Merges Yellow Temperance with Wonder of U, adding calamity manipulation, remote disguises, phasing, teleportation, and independently operating clones. 182
Beyond ordinary Special Grade	242	Masamichi Yaga concludes that Hiyage's strength has surpassed that of an ordinary Special Grade. 242

Background / History

Miyauchi Hiyage is a transmigrator in a world where multiple anime and manga settings coexist. After receiving a magical diary that grants daily rewards, he begins recording knowledge from his previous life under the pseudonym You Know Who. The diary is also visible to selected heroines, allowing him to warn them about their futures while concealing his own identity. 1 2

His earliest entries mix sincere warnings—such as his wish for Hoshino Ai to remain an active idol—with deliberately inflammatory spoilers about the diary holders' futures. This establishes him as a source of information the girls cannot ignore, despite their hostility toward his methods. 1

As his abilities expand, he operates through disguises, Stand clones, Jerry, and the temporary identity “Tom.” He gradually becomes involved with the Reverse Side World, helps expose the supernatural to Conan, joins the Jujutsu Society, investigates Morioh’s Stand-related dangers, and guides diary holders through the Impression Space. 17 39 221 232

Appearance

You Know Who has no reliable public appearance. Hiyage treats his diarist identity as a constructed persona and routinely prevents witnesses from retaining identifying details.

• As a maintenance worker at Toyonosaki Academy, he appeared so ordinary that a guard could recall only his height, build, and skin tone. 25
• Yellow Temperance can alter his body, face, and voice to support disguises. 17
• His Wonder of U clone can assume the featureless “little black person” silhouette associated with an unidentified culprit. 182
• He can also alter facial muscles through Ripple Chi Kung, making himself and others unrecognizable without conventional makeup. 250

Personality

You Know Who is playful, provocative, and unusually fond of revealing information that destabilizes people. He taunts Kasumigaoka Utaha in the Diary Fan Club, seizes the group owner’s permissions, activates a global mute, and leaves before anyone can respond. 18

Behind that deliberately irritating presentation, he is cautious and strategic. He initially resolves to hide his identity and supernatural nature to avoid attracting hostile forces, later using disguises, intermediaries, and clones to keep his movements difficult to trace. 2 17 182

He can be manipulative when testing or recruiting people, as seen in his conversation with Conan. However, he also provides practical aid: helping Shiho Miyano escape the Black Organization, arranging protection for Mai Sakurajima, and giving diary holders training and tools to survive the escalating supernatural world. 39 100 162 176

Abilities & Skills

Magical Diary

A daily-reward diary and the foundation of You Know Who’s influence.

• Grants him supernatural rewards for writing entries. 2
• Is visible to selected heroines, who can read his warnings and spoilers. 1
• Lets him communicate indirectly with diary holders and influence their choices without exposing himself.
• His arrival in the Diary Fan Club demonstrates authority over its group permissions. 18

Pure Yang Body and Ripple Chi Kung

A superhuman physique empowered and stabilized by Ripple.

• The Pure Yang Body suppresses or repels evil spirits. 2
• Ripple Chi Kung regulates the body’s excessive yang energy and can stimulate plant growth. 4
• He can conceal most of his Pure Yang Body and Ripple signatures, leaving only slightly superhuman physical strength visible. 113
• At seven percent unsealed output, he can overwhelm Shinomiya Kaguya through superior control of Ripple’s properties. 143
• His Pure Yang Flame has particularly strong suppression against Cursed Spirits. 219

Destiny Power

An awakened ability tied to fate, spatial movement, and misfortune.

• Perceives fragments of fate and nearby threats through glowing golden eyes. 113 232
• Teleports himself and other people; he can travel roughly ten kilometers in two seconds and perform up to five consecutive jumps. 166
• Gives him a broad field of perception that can reveal otherwise hidden observers. 166
• Can influence opponents through subtle misfortune, causing flaws even in Satoru Gojo’s Limitless technique. 219 220
• Malicious attempts to attack him can draw targets into a “Calamity Torrent.” 231

Yellow Temperance: Wonder of U

A fused Stand combining assimilation, disguise, and calamity.

• Yellow Temperance devours and assimilates organic matter, grows through consumption, and can reshape itself over a host’s body. 17
• Can mimic Ghouls and form a bandaged “bandage man” costume. 167
• Wonder of U adds remote disguises, wall phasing, teleportation, and clone creation. 182
• Creates independent “little black person” clones that can act as vanguards with Special Grade power. 182
• Can invoke calamity against people who think about or pursue him, though active calamity marks require the main body to be near the target and remain limited by his mental power. 184

Unlimited Blade Works and Projection Magic

A weapon-forging and replication system connected to Hiyage’s internal world.

• Projects weapons and can restructure their composition inside Unlimited Blade Works. 221
• Copies a weapon’s previous user’s experience and muscle memory through Projection Magic and reinforcement. 151
• Stores copied cursed tools and materials from Jujutsu High’s treasury. 170
• Can project Black Rope and learn Miguel’s techniques from it. 175
• Possesses the Dragonslaying Holy Sword, which helps him temporarily suppress Tohru’s attacks. 166

Swordsmanship and Martial Arts

A rapidly acquired combat style built around copied experience, breathing techniques, and exceptional physical talent.

• Learns Water Breathing on his first attempt after receiving instruction from Shinomiya Kaguya. 143
• Uses Water Breathing forms including Flowing Dance, Striking Tide, and Whirlpool. 152
• Switches to Thunder Breathing during his spar with Maki Zenin. 152
• Defeats Special Grade Ghoul Kamishiro Rize with Sun Breathing before she can lose control. 166 167
• Learns and teaches Kusanagi-ryu Ancient Martial Arts, including external styles usable without the Kusanagi bloodline. 162
• Rapidly assimilates Zenin-style physical techniques and later defeats Maki in hand-to-hand sparring. 151 170

Equipment / Weapons / Items

• Magical Diary — daily-reward diary visible to selected heroines. 1 2
• Grudge-Seeing Lens — lens given to Conan so he can perceive supernatural entities. 38
• Dragonslaying Holy Sword — weapon used alongside Unlimited Blade Works against high-level opponents. 166
• Black Rope — copied through Projection Magic; he gives a short piece to Yotsuya Miko as a bracelet. 175
• Otherworld Navigation App — reward that grants access to the Impression Space. 125
• Jewel Sword — a powerful Mystic Code used as a transformation device and superior replacement for the Kaleidoscope staffs Ruby and Sapphire. 200

Relationships

• Kasumigaoka Utaha — One of the first readers of his diary; she is angered by his spoilers and taunts, yet repeatedly attempts to identify or contact him. 1 18
• Shinomiya Kaguya — Diary holder, ally, and persistent investigator of his identity; she teaches him Demon Slayer swordsmanship and continues to suspect that he is You Know Who. 143 164 250
• Jerry — Subordinate hired in exchange for unlimited cheesecake; serves as a messenger, Ripple instructor, scout, and public-facing intermediary. 26 39 46
• Conan Edogawa / Shinichi Kudo — Recruited under the temporary alias “Tom” to investigate supernatural threats and the Black Organization. 38 39
• Maki Zenin — Sparring partner whose weapons and techniques help him test Projection Magic and develop his physical combat ability. 151 170
• Satoru Gojo — Mentor and high-level sparring partner; their match allows Hiyage to study Limitless and Domain Expansion. 219 221 222
• Tohru — Powerful sparring partner who exposes the gap between Hiyage’s current abilities and truly overwhelming physical strength. 155
• Yotsuya Miko — Jujutsu ally entrusted with a Black Rope bracelet; she can perceive changes in his body that most others miss. 151 175
• Kishibe Rohan — Morioh contact whose attempt to use Heaven’s Door on Hiyage’s clone ends in injury; Hiyage later plans to help him confront Morioh’s threats. 185 192

Story Role / Major Arcs

• Diary Revealer — Begins anonymously publishing spoilers and warnings that alter the diary holders’ expected futures. 1
• Diary Fan Club Provocations — Appears in the group chat, taunts Utaha, and becomes the central target of the girls’ identity investigation. 18 25
• Conan Recruitment — Introduces Conan to Grudges, exorcists, and Jerry, then offers him an unofficial role as a “savior” under the name Tom. 38 39
• Jujutsu High Training — Demonstrates Destiny Power, studies swordsmanship, spars with Maki Zenin, and is eventually admitted into the Jujutsu Society. 151 153 221
• Ghoul Incident — Defeats Kamishiro Rize, absorbs part of her RC Cell Sac through Yellow Temperance, and attracts Ryomen Sukuna’s attention. 166 167
• Calamity Evolution — Fuses Yellow Temperance with Wonder of U and deploys a clone to explore dangerous areas without exposing himself. 182
• Morioh Investigation — Investigates Stand meteorites, meets Kishibe Rohan, eliminates Yoshikage Kira, and monitors potential Stand awakenings. 188 192 232
• Impression Space Guide — Assists diary holders with Palace exploration, Shadows, Persona awakenings, and the recovery of cognitive treasures. 206 216
• Gojo Sparring Match — Forces a flaw in Gojo’s Limitless through calamity, studies Unlimited Void, and ends their battle without a decisive victor. 219 220 221 222
• Stand Awakening Crisis — Helps Kato Megumi identify her Stand, then teleports to contain Shadow Gotou Hitori’s disturbance while Kaguya and Yukino intensify their investigation into his identity. 248 250 251

Trivia

• The original name 神秘人 literally means “Mysterious Person.”
• His alias “Tom” is used specifically during his first direct alliance with Conan. 39
• Despite presenting himself as an elusive adult traveler in early diary entries, he is a sixteen-year-old high-school student by the time he joins the Jujutsu Society. 18 221