Day 1:
It was almost like disapparating, as some force pulled him to whatever first day he would have to live through. Harry shook off the feeling as he looked around. He was still in the forbidden forest, but there was a different feel to it altogether. The centaurs walked about the grounds more freely, several stopping to regard him oddly, and other creatures were watching him from nearby. Without any further instruction he began walking to where Hogwarts stood above the horizon.
Once leaving the forest Harry noticed the first big difference. Hagrid's hut didn't exist. The pumpkin patch was there, and even a small feeding area for the thestrals, but the hut wasn't there at all.
"It hasn't been built yet," The young version of Tom was next to him. "Don't worry, you're invisible today, not silent, but invisible. No matter what day we're in, no one will hear or see me."
"Why hasn't his hut been built?"
"The school doesn't have a gamekeeper yet."
Harry furrowed his brow, "What year is it?"
Tom smiled, "That should have been your first question." He looked around the grounds, "I've brought us to the year 1943, June 13th to be exact."
"Wasn't that while you were in school?" Harry asked, trying to think about why the date sounded familiar, Tom nodded and started leading him up to the castle.
Walking into the school he could tell it was early morning, students flitting about the hallways, and a few familiar faces were among them. Dumbledore was easy to pick out, and the previous Headmaster Dippet less so. A group of older students began filing out of the dungeons, among them was the teenage version of Tom Riddle that Harry began following. The horcrux didn't correct him, so Harry assumed this was who he was supposed to be following for the day. On the second floor, he broke off from the group.
"We had Arithmancy or Divination, and back then the Arithmancy Professor was easily persuaded to forgive tardiness." The horcrux explained.
"Divination may have been worth your time." Harry muttered.
He was surprised when the horcrux laughed, "That may be true." When harry looked at him funny, "There's a reason people aren't usually horcruxes, we become more like our host the longer we're with them."
The halls were all but deserted, and the Tom Riddle wearing the Prefect badge was herding younger students to class, but staying on the floor. When there was no one left he walked towards the girl's bathroom near the stairs. Tom tapped his wand against the door, and Harry recognized the Hominum Revelio that showed the bathroom was indeed empty. Harry followed him in and watched as he entered the chamber of secrets for only a minute before closing the chamber and heading to class. Harry didn't even have time to follow him. He moved to follow Tom, but the horcrux stopped him.
"We aren't here to sit in on a Arithmancy class. We stay here and wait to see what the basilisk does." Harry felt uncomfortable leaning against the wall of a girl's bathroom with someone who looked eleven. Perhaps in his own time no one used the bathroom, but in this year there were girls in and out constantly for the three hours that he waited for the basilisk to emerge from the chamber.
It was during lunch that the steady stream of girls using the toilet changed, there was a high pitched cry right outside the door, and it clicked. Harry looked at the horcrux, "No,"
"Yes," Young Tom answered softly as a Ravenclaw ran into the room in tears, Myrtle. She didn't look much different than she did as a ghost, and she certainly didn't sound any different. He knew why today was so familiar, today she would be killed by the basilisk, and he had to watch. His stomach dropped as he heard the snake hissing to open the chamber from the inside. There was a hiccup from Myrtle that hid the noise, but she kept on crying as the chamber opened completely. The basilisk was a little smaller than it was when he fought it, but now he could look in its eyes.
The eyes shifted to the stall that Myrtle was hiding in, and without thinking, he hissed back at the snake, "Don't kill her."
For a moment the basilisk turned its eyes on him, but flicked back as the stall opened. It moved towards Myrtle, and she sniffed before talking through her tears, "Don't you know this is the girl's-"
She was dead as soon as she looked up. Harry remembered her saying she heard strange hissing, and that she'd left her stall to tell the male voices to get out of the bathroom. But Tom wasn't here.
"He never was here when she died," The horcrux explained as the basilisk retreated into the chamber, closing it with a soft hiss, "I never knew what that snake was talking about when he said there was a boy he couldn't kill. I guess you were always here to get her killed."
"So if it wasn't for me, she'd be alive?" Harry paled at the thought.
"No, the basilisk would have waited her out. You just made his job easier." Tom watched as the door opened, "Now that she isn't crying, the other students think that she's left. This should be interesting."
A group of five girls that looked to be sixth or seventh years came in talking, and from the noise outside the bathroom, it seemed to be between classes. One of them screamed as they saw the body, most of them freezing in place as they caught sight of Myrtle's body, there was some blood from where she hit her head on the tile floor when she fell. One of the girls moved forward and dutifully checked for a pulse, Harry caught sight of the Head Girl badge she wore as she looked to her friends, "One of you fetch a Professor, Dumbledore should be closest." He recognized the voice, "Well, get on with it!"
A couple of the girls stepped into action, leaving the room in a hurry as the other two looked away. Harry looked to the Horcrux and mouthed, "McGonagall?" A grin and a nod was his response.
There was a commotion as Professor Dumbledore walked into the room looking concerned, and his eyes caught on a young Minerva McGonagall that trying to keep her emotions at bay. He waved the other seventh years from the room before talking to her, "Is it another petrification, Minerva?"
"I don't think so," She said, the command in her tone was gone, and for once Harry saw her as being a kid, now kneeling by the dead body of one of her peers. "The others were rigid when they were petrified, and she..." She held up Mytle's hand, that flexed with the motion.
Dumbledore covered her hand, "Thank you for doing so well to stay calm. Now, I need to ask one more thing of you. Tell Headmaster Dippet to meet me here, and then go to the hospital wing to get a calming potion. I'll let your teachers know you have the afternoon off. Can you do that for me?"
Minerva took a shuddering breath, and masked the fear on her face as she nodded. She stood and marched out of the room with the determination that he had always seen in her.
"Professor..?" Myrtle's voice rang out in the bathroom, and Dumbledore looked up to see the version of Myrtle that Harry knew all too well. She looked at her body with an odd sense of fascination, "Wh-what's going on?"
"It seems the monster has taken you as its victim." Dumbledore said softly, "You have been killed, my dear."
Other teachers began making their way in, followed by the Headmaster. Myrtle didn't even cry though, seemingly shocked beyond emotions as she floated above the sinks circling her own body in a protective manner. Her father eventually showed up, and she followed her body when it left the bathroom. Harry followed the group, noting that Tom was helping keep students in the great hall, and the carefully sculpted look of despair on his face. A voice rang out above the others, and Myrtle's attention turned to him. She tore away from the group and into the Great Hall.
"She torments Oliver Hornby for two months for today. She believes he is at fault for her death, because if he hadn't made her cry, she wouldn't have been in the bathroom in the first place." Tom commented, "Eventually the Ministry has to step in, and they convince her to return to her toilet."
"How much more do I have to watch?" Harry whispered.
"You've already had to watch Hagrid be expelled, so I think we can be done with today. After all, today you had it easy." Tom smiled as they both disappeared from the room.