Boku no Risou no Isekai Seikatsu

He becomes a kemonomimi boy in the new world after orgasming

A nameless 40-year-old single man loses consciousness from masturbating too much and thinks he has lived his life to the fullest, but when he regains consciousness he sees a cute girl with a worried look on her face in front of him. Her name is Misha, and she calls the man Norun. According to Misha, he had nearly drowned in the river. The man does not understand what is happening, but what he sees reflected in the water is the image of a cute boy with animal ears. The man is reincarnated into another world and becomes a person called Norun. The inhabitants of this world have animal ears and tails, there are more females than males, and it is a polygamous society. And Misha is the girl who will become Norun's first wife. Although they are not yet married, Misha lives with Norun, and does not hesitate to take off her clothes and take a bath with Norun. As Misha washes Norun's body, his crotch begins to swell more and more.

(Source: Getchu, translated)