Okitsune Nakadashi Ongaeshi ~Onee-san no Naka de Ippai Kimochi Yoku Natte ne~

Our hero is a college student who lives in a rural town.
One day he comes across a wounded fox, which he treats. Then a naked woman appears before him, claiming she is the fox and that she wants to return the favor.
That is the beginning of a life with the big breasted fox girl, who repays the favor by letting him ejaculate inside of her as much as he wants.

[From English DLSite]