Toshishita Chin Kui Oba-san

I hate grown men. But I love younger men.
Akiko Furukawa, a 35-year-old unmarried woman, loves Shun, a younger man who lives in the same apartment building. Akiko masturbates in her fantasy to suppress her desire to fuck Shun, but one day, when she finds Shun's weakness, her suppressed desire goes out of control and attacks him... Shun is too shy and scared to do anything but surrender himself to Akiko, but when he learns about the female body and its pleasures, he becomes Akiko's prisoner, and he becomes a male who shakes his hips and seeks pleasure as he pleases his instincts...!

(Source: Fanza, translated)