Sore wa Tada no Senpai no Chinko

Synopsis

In a world where penises can be safely cut off—regenerating in mere weeks—people lead very bizarre lives. While separated from their original body, penises become sentient and are able to continue living, allowing them to be sold off or even kept as pets. However, penises cannot live separated from their bodies forever. If not returned to its body after a certain period of time, the penis can die—often making their longevity quite short. Despite this, penises are popular and continue to be sought after by many people for various reasons. (Source: MyAnimeList)