Ayase Kokoro’s Mom remarried an older guy named Oshima, and Ayase immediately hates his guts.
This one time, the Mom goes away on a multi-day trip, and Oshima reveals his true nature: He roofies Ayase with aphrodisiacs to have his way with her.
The thing is that the drugs worked too well, and she ends up crazed for sex and creampie. The bastard Oshima couldn’t get enough.