@WashedOutGundamPilot Weird speculation on my part, but it works as a sort of "revenge" fantasy, only instead of besting some guys in sports after years of toil and perseverance, you get a girl (or girls) who you can easily domineer due to the natural physical advantage men get after puberty.
I have no idea what this source material is, but my guess is all the former bullies are into this guy now, so he gets a harem. That also works for a triumphant comeback story, perhaps.