2
Six months prior to the beginning of the final battle, Lucius Malfoy had found a spell that would restore Tom Riddle's diary - and thus Tom Riddle's spirit - to how the spirit was when he first entered the diary.
Unbeknownst to Lucius, however, Tom Riddle wasn't evil when he created the enchanted diary. He was, actually, just a lonely sixth-year with no one to call friend who had decided to just create one instead. The part of Tom Riddle that first went into the diary was the innocent, pure soul of the true Tom Riddle.
Unfortunately, putting part of his soul into the diary left it's repercussions. With only half a soul, the body of Tom Riddle grew evil. That part of Tom Riddle was the part that became Lord Voldemort.
After being restored to the diary, and with an additional spell to remove him from the pages of his prison, Lucius learned this the hard way. Intending to bring another Dark Lord into the world to aid the true Lord Voldemort, Lucius Malfoy had instead brought to life the most powerful ally the light side would ever receive, aside from Harry Potter himself.
To atone for his rash actions born from loneliness, Tom Riddle went immediately to Albus Dumbledore in hopes of receiving asylum. He got it- at the price, again, of his freedom. Dumbledore made the quick decision of making sure Tom could never harm innocents again and bound him to the one Tom Riddle had five times tried to kill. In other words, Harry Potter.
Needless to say, neither were very happy at this predicament.
What the two didn't know, however, was that by binding Tom to Harry, their souls could never be separated, not even by death. It had aided Dumbledore's plans greatly, something the two would not find out until it was too late.
But there was a flaw in Dumbledore's plan. In order to sacrifice the powers of the two students to destroy Lord Voldemort, their powers would have to be warring with each other. At first, with the constant bickering, it seemed to be working. But then came the unexpected attack on Hogsmeade, an attack that killed fifteen students, ten Aurors, Hagrid, and countless civilians, but also nearly killed Harry himself.
Tom, being the cause of the attack as Voldemort wanted revenge for Tom's refusal to join the Dark, felt so guilty about it that he would not leave Harry's bedside for two weeks, the time it took for Harry to heal. It took Harry another two weeks, and a confession of growing attraction for the other boy, for Tom to break out of his haze of guilt.
Again needless to say, it was hard not to find one without the other.
And now, two months after the confession, the true Lord Voldemort had attacked Hogwarts. The battle was vicious and bloody, both sides receiving their own equal amount of casualties. Harry had been forced to the frontline, like he knew would happen three years prior when Lord Voldemort had risen again. Tom had wanted to join him, but being not truly corporeal would make him next to useless and thus Harry had forbidden him.
It seemed that whatever those spells had been had returned Lord Voldemort to an age where he was nearly defenseless, the age Tom Riddle was when he created the diary - and rejoined the broken halves of one pure soul.
"Well this is interesting," said a voice to his right. Harry looked up sharply, reaching somewhat awkwardly for his wand. Before him was a man of medium height with extremely short dark brown hair and a receding hairline, wearing something very... strange. He looked at the two with amusement. Harry narrowed his eyes.
"Who are you?" he demanded. The man raised his eyebrows, looking insulted.
"Well, no need to get huffy," he said in an affronted voice. "You know, you could use some manners. I know just the person to teach you." He snapped his fingers and Harry blacked out.