Iona

Shu Endo is a fifth grader at Konomiya Elementary School. When their homeroom teacher goes on maternity leave, a beautiful but mysterious woman, Iona Igarashi, is the substitute. She is dressed in a sexy fashion unlike a typical school teacher, and she speaks her mind frankly. Shu and the other kids are constantly being pushed around by her. Moreover, Shu becomes Iona's "favorite" and......? (Source: Bunshun Books, translated)