Oji-san to.

"So, do you want to do something more amazing next time?"
"Something more amazing?"

Using the excuse of tutoring her as a pretext, an older man gets Saki to pass by his house. Ever since she was small, he has been thoroughly teaching her the pleasures of being a woman.
One day, after she passed the exams for her school of choice, Saki got a promise that she would at last get his dick in her; On the day of the school entrance ceremony, at this older man's house...

A pure and innocent girl who had pleasure instilled into her, without her mother knowing, will be turned into a woman.

(Source: DMM)