TSF Monogatari is a two part hentai anime series based on the manga of the same name. It is about a guy who suddenly collapses and is taken to the hospital due to undiagnosed cancer. Once at the hospital it is found is chances of survival were slim unless he agreed to take part in an experimental cure that just so happens to change his gender as well. He agrees to it.
Next we seen him at his school being reintroduced to is classmates with an explanation for the gender swap. He is still wearing his male school uniform at this point. Of course the first thing all the guys in the class want is for him to let them feel his breasts, and he reluctantly gives in and gets some serious fondling. After school, one of his female school friends offers to lend him some of her clothes so he can blend in a bit better so they go back to her house and we see our hero trying on some underwear.
Later he shows off being female to a group of his classmates outside a convenience store and, unwillingly at first, gets fondled more than he would like but he comes to enjoy it and ends up giving the guys blowjobs.
Well, from there on he becomes a nymphomaniac and in true hentai form gets sex wherever he can.