Eh. This doesn't have much of a plot. Just a setting for the romcom. I suppose the author did take an extra step by explaining how Komine returned to the past, but I kind of doubt there's anything deep about it. It's not like he would be in the past because there was an apolocalypse happening in his original timeline and he needs to change the future to avoid the end of the world. He just needs to collect idol photos for a space alien in exchange for a second chance with his love interest. It's more like a joke than the beginning of a grand adventure or a battle against impossible odds.