Parallels

All Toshinori Yagi-formerly known as the Number 1 Hero All Might-wants to do is train his young successor to be the hero into the greatest the world has ever seen. But when a training exercise pushes Toshinori into a parallel universe, he has to find a way to get back to his boy as soon as possible. Or: All Might gets a peak into what it's like if he'd never met Izuku...