Let's see if someone here can remember the name of an hentai comic I read some years ago.
PLOT:
Scholars on a trip, one of them (a boy) decides to go to a place where a warm water spring is creating a small hot water natural pool between rocks. Two girls unexpectedly join him and after a while he gets hard looking at them. One of these girls cannot ignore the fact he is getting hard and literally assault him all in a sudden splashing the face in the water surprising everyone, seeking for a raging blowjob but the other girl (who probably is sentimentally involved with the boy who doesn't know about this) stops her. In the end however the three of them obviously end up having sex together and they probably will do it again in the future.

Does this remind something to anyone?