The End of Puberty 2011 one on netflix

In a noisy classroom, biology teacher Madoka proceeds with his lesson in a small voice.He is unable to look the students square in the face nor admonish them for talking or sleeping in class. Only Tsubura looks upon him with a smile. Very much infatuated with Madoka, she records his idiosyncrasies in her biology notebook through illustrations–tapping his hand on his chin is proof that he is annoyed; messily tugging at his hair when he is at his wits’ end. Tsubara, fearful of being forgotten after she dies, only eats things loaded with preservatives so that even if she dies, her body will not rot. Believing such things, Tsubara, thinking that «combining Mr. Madoka who has no one with me who needs someone would surely be perfect,» gets the wild idea of a genital exchange with Madoka.