I think it was easy to follow. o: Chiaki wanted some excitement in his life since he’s not very social etc. So he went with the flow and attended an orgy session. Became friends with them, had casual sex with them (sex to them is an open thing, they don’t equate it to love, it’s to have fun and everyone is having a good time). Got attracted to one of them aka Taiga, guy in the cover. Taiga on the other hand has been faintly attracted to Chiaki from the start but he’s never been in a proper relationship before so he’s not very good with identifying his feelings. Cute dates happened, feelings were realized, Chiaki finds out he’s bi, Taiga wants an exclusive relationship, and they eventually became a couple. So they won’t be attending the orgies anymore or have casual sex with others because they found each other. Yeah, that’s it. U: Simple, right? No drama or angst, no sad past on either sides.
Nothing really seemed to make sense...kinda weird