Choukyou Diary

"Since I was young, I've kept a diary".
Ever since starting to date him, all I've written about are things about him.
All my memories with him, each and every one of them are important, and I just can't imagine that I would ever be able to forget them.
Or so I thought, but now I'm going through my diary, turning the pages and reading them in order to get a vivid memory of what that time was like.
And what I found in my happy but also embarrassing past was... all in my diary, a diary for my eyes only, in which I spelt out all the things that he and I did in those days we spent together, in complete and utter frankness...
Schoolgirl Kyoko's first boyfriend was an older guy, who was already working full-time. Usually, they should have been meeting, falling in love and getting closer to each other, but...
"You must dedicate yourself completely, mind, body and soul to me. I'm not satisfied with just your love. I want your unconditional faith and loyalty. Give all of yourself to me, and accept all of myself in return. Can you do that?"
What he was saying was absolutely ridiculous. Compared to such a level of devotion, the idea of being simply lovers paled away to nothing.
It wasn't a sweet kind of relationship that he dreamt of when he determined that Kyoko would save herself and give her virginity to him.
Steadily losing her bearings as they continue to go on dates, and as the activities they engage in become more hard-core, Kyoko gradually begins to weaken, both mentally and physically.
And then recently, her little sister Choko falls prey to the clutches of Kyoko's boyfriend, despite already knowing about her older sister's sex life. Thus, he begins training in double time...
What will be the shocking conclusion of the training received by the two sisters......!?

[From DLSite English]