Has this been done before? Sure. Has it been done like this? No. Fucking. Way.
Hope you enjoy.
I am Lord Voldemort. Harry stared at the fiery words in abject horror. His lifetime nemesis was standing not thirty feet away from him with a smug look on his face, and he was powerless to do anything about it. Less than powerless actually. He was at the mercy of this man, and he knew it.
“You see, Harry, Lord Voldemort is my past, my present, and my future.” The last word was uttered in the long, sibilant hiss of parsel tongue. “How could you, a mere child still in diapers and unable to survive without your pitiful mudblood mother, defeat ME, the most powerful wizard that this world has ever known?! Hmm? Can you tell me?” Harry was frozen in place by the eyes that were so similar to his own, yet very different.
“Dumbledore says it was love.” There was silence for a moment before Riddle burst out laughing.
“That old man is senile. Forget about him, Harry. You will see him no more.” Anger rose up in him like a poisonous steam, both freezing and blazing hot at the same time, pushing adrenalin through his veins.
“Dumbledore. Is not. Senile.” The teenager only looked on with a dark smile.
“So you say. But where was he when you were locked up in your little cupboard, at the tender mercies of your relatives? Hmm? I'll tell you where he was. He was in his office, sucking on his lemon drops like the old fool that he is. He did not think to check on me when I was an orphan, so obviously bullied in my childhood, and he did not think to do that for you either. You and me, Harry, we're more alike than you think!” Harry was shocked that Riddle knew so much about him, and appalled at the comparison between the two of them.
“No we're not!”
“Oh, but we are. The only difference between you and me is that of circumstance. If our positions had been reversed, you would have gone to the great house of Slytherin. You would have delved into the deeper magics, those that carry real weight. And you would have become just like me.” Harry tried to deny it, tried to ignore the awful truth to Riddle's words, but to no avail.
“Fuck you!”
“Ahh, such a dirty mouth for one so young. Perhaps some manners need be introduced. Imperio!” A red beam shot out of the end of Harry's own wand and hit him in the chest before he could react. A weight settled over his mind, bidding him to do the elder teenager's will. It wasn't uncomfortable, necessarily, but it didn't feel right in any sense of the term.
“Now apologize, dear Harry.” He tried to fight it, but it was to no avail – he was truly caught within Tom Riddle's web.
“I... I... I apologize.”
“That's better. But now, I must decide what to do with you. On one hand, you have displayed extreme foolishness and perhaps even stupidity coming down here to do battle with the monster of Salazar Slytherin, and all merely for an eleven year old girl of no consequence. You're stubbornness apparently knows no ends. You are obvious to the extreme in everything you do, and do not apparently care of other's opinions of you... and yet I can sense a bit of myself in you. I sense the same darkness that I once had at the same age, although it is admittedly far less pronounced in you. But with the proper grooming... What have you to say about all this?” The imperio forced him to remain silent.
“Ah, I apologize Harry. You have nothing to say as you are merely an extension of my will. Now. Let us see what you are truly made of. Kill the girl. And please, do try to do it... creatively.” Riddle tossed Harry his wand, unworried about the still naïve and unpowerful boy breaking loose of his spell. Harry turned his head and observed Ginny lying prone under the “greatest of the Hogwarts Four” statue. She was deathly pale, and she did not appear to be breathing, although such a thing was difficult to tell through Hogwart's voluminous robes.
“Wingardium Leviosa” Waving his wand in the pattern dictated by the aforementioned spell, he watched as Ginny rose up towards the jagged ceiling. The tumult of feelings he would have expected to feel were gone, replaced by something else, something darker, but only underneath the blanket of the imperius curse. Higher and higher she rose, until she was just barely pressed up against one of the extremely sharp stalactites. She seemingly paused there for a moment, but if one were close enough he or she could tell that the magic that was pushing her up was struggling against the natural formation of rock. In the end, magic won out and red fluid began to pour down in torrents to the floor of the underground cavern, covering it in a dark, sickly sheen of blood.
“I did say creatively, but that will come with time I suppose.” Harry turned to look at the elder boy blankly.
“Yes, Harry. With time you shall become my... apprentice.”