Musomosomo Sei Syndrome

Itou is a young man who, so to speak, has no materialistic desires, drive to succeed or libido. Anyway, he has no enthusiasm and desires nothing. Ever since he graduated from college, his job hunting effort has never gone well due to his lack of enthusiasm, and he has done nothing but diminish the savings stored up in his bank account.

One day, he kicked a Jizou statue by the side of the road in a fit of irritated anger after another failed job interview. He gets enveloped in a mysterious flash of light while hearing an angry voice.

Itou rushes to board the last train of the day while beset by strange thoughts. Sitting across right in front of him was a defenseless high school girl who has fallen asleep, tired from school. As soon as he laid his eyes upon her, libido began to surge from deep inside him all of a sudden — to a degree that he's never ever had before — and he got an erection.

"You will rot if you leave that erection alone", whispered a mysterious voice to him. Leaving it up to the voice to tell him what to do, he approached the sleeping girl whose steady breathing he could hear and found himself undressing her uniform. Naturally, the high school girl wakes up as he uses his member to penetrate her slit...!

(Source: BookLive, translated)

Notes: Originally serialized under the title Zesshokukei Danshi, Seiyoku wo Shiru (絶食系男子、性欲を知る), Volume 1 compiles chapters 1-8, Volume 2 compiles chapters 9-16, Volume 3 compiles chapters 17-24, Volume 4 compiles chapters 25-32.