Takurou has failed his med school entrance exam for the fifth time.

Maybe it was because of all that stress that he developed a sex addiction, and his mother will end up having sex with him everyday.

Mai, his mother who's now over forty years old, has grown visibly tired of her son, who for years would lust after her body everyday, demanding sex without a single care about what place they were in...

(Source: DLsite)

[Note: This has 2 near-identical versions, one is the original doujinshi, the hardcore version which is a single book that has mosaic censorship; the other is a heavily censored softcore version, split into 2 chapters and published by DEEPER-ZERO; The covers are slightly different but the story is the same.]