Ano Oni Kyoushi ga Boku no Ane ni Narun desu ka?

When a young boy learns that his father is remarrying, he is thrilled at the prospect of finally gaining an older sister. His excitement, however, comes to an abrupt halt upon discovering the shocking identity of his new stepsibling: Shina, his school’s notoriously strict physical education teacher. The revelation turns what should have been a joyous family milestone into a source of profound dread, leaving him to grapple with the reality that his fearsome instructor is now officially part of his family. The situation grows even more complicated when his father departs to live with his new wife, leaving the boy to share a household alone with Shina. Forced into close quarters with the very teacher who terrifies him in the hallways, he braces himself for a tense and uncomfortable domestic life. Yet, as they navigate their unexpected living arrangement, he begins to witness a side of her that no one at school has ever seen. Away from the whistle and the gymnasium, the intimidating PE instructor transforms entirely. At home, Shina is surprisingly clumsy, easily frightened by insects, and genuinely kind-hearted, revealing a stark contrast between her professional persona and her true self.