I wanted to undress Mikuru-chan, so I got the idea to play strip mahjong.

Your premise and conclusion are both baffling.

But Koizumi-kun was there, and he always loses at games, so taking that into consideration, I changed it so that the winner gets to pick who undresses.

Why do your course corrections always end up being a full reversal?

So then Yuki would win, and she only ever chose Koizumi-kun.

And that's why Koizumi-kun was is currently in the club room in nothing but his underwear.

Getting a scolding.

Sympathetic Nagato-san