Nanami's friends mock her and call her "Nanami-chan" because she looks feminine. As a test of courage, she decides to investigate one of the seven mysteries that are passed down at the school. There is a rumor about "Hanako-san of the Toilet" who lives in the toilet on the third floor of the old school building. Nanami heads to the toilet to find out the truth of the rumor, but... there, Nanami's body is enveloped in a mysterious light and turns into a woman's.