Harry Potter is the Master of Death, and thus, immortal. Every couple thousand years, he'll let himself reincarnate into a new dimension. This dimension is quite similar to his first one, except he has a twin brother, and the Voldemort in this world is willing to give up everything he's worked for, as long as Harry teaches him magic. And Harry? Harry just likes annoying Voldemort with memes, vines, and Potter Puppet Pals.