Man, without the parallel world fantasy shit, this is already so good. But with the fantasy shit, this is just *chef kiss*.
Anyway, it happened when seme accidentally overheard uke's department about how uke's junior shouted teasingly that uke was looking for someone to date. Seme and another girl raised their hands, but uke chose seme (safe choice lol).
The parallel universe thing happened because of the strange stones some fortune tellers sold to the both of them. Uke swapped with himself from another world, a world where the first event, he chose the girl (or more like seme didn't accidentally hear the whole thing).
Ookami wo Katte imasu