JJK OC Maker & Creator

Japan has only two jujutsu schools, Tokyo and Kyoto Jujutsu High. The Tokyo campus hides in the mountains on the edge of the city, posing as a Buddhist temple. Students usually start at Grade 4, go on missions with a supervising sorcerer and may customize their dark uniform. Once a year the schools meet in the Goodwill Event, where the only rule is no killing.

One scale ranks sorcerers, curses and cursed tools: Grade 4, 3, 2, 1 and Special Grade, with semi-grades in between. The series puts it in weapon terms: a wooden bat handles a Grade 4 curse, a tank might not be enough for a Grade 1, and cluster bombs only might work on a Special Grade. Sorcerers take missions that match their grade and earn more as they climb.

Most sorcerers are born with an innate technique that shows up around age five or six and makes up about 80% of their skill set. Some run in the big clans, like the Gojo family's Limitless; others appear in families with no sorcerers at all. The technique itself never changes, but sorcerers keep inventing new moves built on it.

The pinnacle of jujutsu. The user forms a hand sign and seals the target inside a barrier built from their own innate domain, where every technique they cast is boosted and guaranteed to hit. Even most Grade 1 sorcerers never master a lethal domain, so a Domain Expansion should be rare and hard-won for an OC too.

A binding vow is a contract with yourself or with someone else: accept a limit, gain power. Explaining your technique to an enemy makes it stronger, and Kento Nanami caps his cursed energy during work hours so he hits harder in overtime. Breaking a vow carries a penalty. A Heavenly Restriction is a vow forced on someone at birth, like Maki Zen'in's missing cursed energy traded for a superhuman body.

Sorcerers who use jujutsu to hurt people. Some pick it simply because it is an easier life than exorcising curses for Jujutsu High. A branded curse user can be treated like a curse and marked for exorcism, and bounties are common in the jujutsu underworld. Suguru Geto became one after he was expelled from Tokyo Jujutsu High.

Curses form from the cursed energy that leaks out of people's negative emotions, and non-sorcerers cannot see them. Many look like monsters from Japanese folklore: vengeful spirits, ghosts and yokai. They are graded like sorcerers, and what separates a Grade 2 curse from a semi-grade 1 is whether it can use a cursed technique.

Spirit familiars conjured with cursed energy, usually through a medium such as a paper talisman. Some techniques summon a whole set, like Megumi Fushiguro's Ten Shadows, but even a sorcerer with a weak innate technique can learn to summon simple shikigami. The standard advice for fighting a shikigami user is to go after the summoner.