I posted something similar to this in the "Is Harry A Horcrux?" thread, but I thought it seemed different enough to make a whole new theory and maybe allow others to create a different theory on the connection and whats really in Harry. Please keep it from turning into another "Is Harry A Horcrux?" thread, talk about the other possibilities
I’m going to introduce another possibility that may shock or make you very confused. But first, we must look at what we have come to see what happened that night that Voldemort attacked the Potters. First he killed his parents, Lily sacrificed herself, thus protecting Harry. We don’t know how long it took, but Voldemort turned his wand on Harry, did the AK curse, and it backfired. This left a scar on Harry’s forehead, Voldemort was ripped from his body, and they both now have connection.
One theory I propose is that a piece of Voldemort’s soul was already in Harry because someone else (whether that be Dumbledore, James, Lily……whoever) placed it in him. So when Voldemort did the AK, he essentially hit himself which may be why it backfired (going to where the soul originated, which is Voldemort, and thus ripped him from his body). But we know that its ancient magic. So does that mean anybody who has this ancient magic can live through an AK curse? What if Voldemort tried the curse again before the power goes away, or before he became a new walking, talking, Voldemort? Would it have had the same effects? This would only mean that somebody got a Horcrux, extracted that soul piece, and then placed it in Harry. I don’t think that’s likely, so maybe Voldemort placed it in Harry. That would make absolutely no sense, because he AKed Harry, which would mean his soul piece dies as well, unless theres something in the spell to make a Horcrux that protects it.
Unlikely….
But what about this theory? Its not a soul piece within Harry, but its Voldemort’s imprint left behind. Voldemort was supposed to die that night, but he remained in existence (I won’t say alive because being immortal, I believe, is not alive or dead). When he did the AK, he himself was ripped from his body and left clinging to life. What if his imprint went on its own too? Without a mind to guide it (like the ghosts), since Voldemort is still around, it had to somehow find its way into a living thing that matched Voldemort (“mark him as his equal”) So it went back to where it originated…only it didn’t realize that its not Voldemort since it doesn’t have a mind. Voldemort was able to use this to his advantage in OotP, but didn’t realize what it was until the end, where he may have had second guesses. He was able to access the imprint, now residing in Harry, and give it a mind (but it couldn’t control its actions, which is why we didn’t see Harry walking around killing people or anything like that). Giving it a mind, allowed it to be manipulated by Voldemort. So when Voldemort actually possessed him a the end of OotP, he found out it was his own imprint and stayed away. He retreated to think about the next move to get his imprint back. There might be certain ramifications to not having an imprint.
Did any of that make sense?
And I couldn't think of a proper title, so feel free to ask for it be changed.