一ノ瀬 まつり

The popular and friendly girlfriend of Nobuhiko and his classmate. As an honor student, she excels academically and is known for her love of books. She and Nobuhiko are in-line with another in their personality. At the beginning of the story, she unintentionally swaps bodies with Nobuhiko's older sister after she's just had her first time with Nobuhiko.

It is revealed that the initial body swap between Mari and Nobuhiko's girlfriend occurred a decade ago. Deeply in love with her brother, Mari once confessed her feelings, but he turned her down due to their sibling relationship. Longing for a chance to be with him, Mari made a heartfelt wish to become someone else. As a result, for ten years, the cheerful literary girl known as "Matsuri" is in fact the true Mari. On the other hand, the enigmatic scientist known as "Mari" is the one inhabiting Nobuhiko's girlfriend's body.