Kindergarten Noir is widely known as the world's safest kindergarten. Attended by the children of wealthy and notable figures, its defenses are seemingly impenetrable, even though assassination attempts are a big part of the daily routine. However, the teachers of the kindergarten are far from ordinary—they are all convicted criminals trying to reduce their sentences.

The recently joined legendary assassin named Rita is no different. According to her contract, she must work as a teacher for a full year to be released. Rita quickly proves her worth with unmatched combat skills, but even the notorious assassin has a weakness: she longs for a handsome boyfriend, which leaves her vulnerable in combat when faced with a particularly attractive opponent. Rita and her colleagues continue to ensure the children's safety to gain freedom, but Rita never stops looking for the man of her dreams.