Houkago Nyan Nyan
A hentai about first love and, more importantly, the first time.
The first story, for example, is about an unnamed schoolgirl who has heard a lot about sex, but lacks any experience whatsoever. Interested in everything, she asks her underclassman Yu to fap in front of her. It doesn't take long before the two shake of their embarrassment and do more than just masturbating for each other.