Sore wa Tada no Senpai no Chinko

In the present, women have discovered that it's possible to cut off a man's dick with minimal complications: the removed dick can move around and function outside of the body for a period of time, and will regrow on the man's body after a period of weeks. Thus, business is booming for the creator of a urinal guillotine, and a few high school girls are eager to try them out. Each has their own reason for collecting their classmates' members, but one thing's for sure: they'll lovingly care for their adorable dicks!