Gitai Saimin

Murakoshi Shinta is a student prone to wild delusions. He has kept this hidden all this while, living his gloomy and mundane life. One day, a tentacled alien parasite takes over his penis. Murakoshi complains to it that he is unable to walk around outside, what with his groin exposed, but the alien assures him that no one will notice as it has the ability to cloud people's minds. Thus, Murakoshi utilises that ability to satisfy his desires.