J is a legendary hitman, an orphan raised by a syndicate who became so feared in the underworld for his lethal skills that he is known as untouchable. Megumi is a lonely third-grade girl who is bullied at school for her half-Japanese, half-American heritage and feels unhappy at home under her strict mother. Their lives collide when they accidentally bump into each other on the street, causing them to swap bodies. Now trapped in the body of a small schoolgirl, J must navigate the social pitfalls and academic pressures of elementary school, while Megumi finds herself inhabiting the body of a man wanted by every major criminal organization. She must maintain his dangerous reputation and handle his contracts, all while dealing with the fact that her strict new life as a feared killer is, to her surprise, far more freeing than her original one.

The story is a chaotic action-comedy that follows the two protagonists as they desperately try to keep their swap a secret and maintain each others everyday lives. For J, who never attended school, even basic math is a challenge, and he must learn how difficult a young girls life can be while hiding his own violent instincts. For Megumi, life as a hitman offers a strange kind of escape, and she finds herself enjoying the power and freedom that comes with being untouchable. Their situation is complicated by their respective circles, including J’s handler, Yanagi, and a fellow assassin named Marie, as well as Megumi’s classmates, including her bully Renji who harbors a hidden crush on her. Notable narrative arcs involve J using his new position to eliminate Megumi’s bullies, Megumi taking on assassination contracts for the first time and discovering a talent for it, and the growing threat of outside forces who begin to suspect something is wrong with the untouchable hitman. The series is based on the web manga by Masao Ohtake and serialized on KADOKAWAs Harta Alternative website, with the television adaptation announced in March 2026.