Roshutsu Kairaku ~Mirarete Nureru Osananajimi, Mitama Misao.

Misao and Shingo are lovers who have never gone far beyond kiss.
While they are playing a game at home to kill time, they had an idea of the penalty for the loser. The defeated one has to go out and fetch a drink with no clothing on!
Misao, who became the loser, hesitates at first but gradually turned on by the act.

[From DLSite English]