Albus
Twenty-two years after the war, twenty-two years as a ghost in Hogwarts, and no one, not a single soul, had seen him, after all, he had made it that way. After that wretched war, a lot of new ghosts had appeared in the castle, so it was easier for him to hide and, well, haunt the castle in peace, the other ghost loathed him and didn't interact with him, which suited him just fine. He had watched the arrival of the spawns of Potter with great attention, the first one was just like Potter, except he had hazel eyes, Gryffindor to the core, confident, charming, rather boring in the end. The third, Lily Potter, the only girl, was a menace, Ravenclaw, she was witty and sarcastic and pulled the most ingenious pranks. The second was his favourite, if he had to choose, Albus Severus Potter, an interesting combination of names, the boy was a Slytherin, quiet, analytical, he had helped his sister with some of her pranks several times, he had a passion for books and academics and a great understanding of the inner workings of magic. He reminded him of himself.
And it wasn't a good thing. At all. That's why, after twenty-two years of being completely invisible, he decided to talk to someone. Albus Potter was in his fifth year and had developed a fascination with the Dark Arts, a fascination that was quickly turning into an obsession. Much like himself. The boy had slowly distanced himself from his friends over the year, then from his cousins, then from his best friend, the young Scorpius Malfoy - what a terrible name, by the way - and now he knew that he had had a very violent argument with his parents after the Christmas holidays. He also knew that Albus felt he wasn't accepted by his family, as a Slytherin and as a person who was more versed in academic matters than the people in his family. In short, from that moment on, and especially when Potter found the Room of Requirement, which gave him access to all the most obscure and dangerous books, he decided it was time for him to intervene, and so he followed the fifteen-year-old second son of Harry Bloody Potter into the Come and Go Room.
The boy sat on a deep green couch and began to read the book he had chosen, one about the creation of inferi - very vile and messy this one - Albus had a look of morbid fascination on his face. "I don't recommend this one."
Albus jumped and looked behind him, a ghost was towering over him, he was young and quite handsome, he was wearing a Slytherin uniform. "Who the hell are you? I have never seen you before."
"I'm just a ghost. And I said I didn't recommend this book, in fact I don't recommend any of them until you're at least a fully grown adult. The Dark Arts are fascinating, I won't deny that, but they're also quite destructive. In fact, it's partly because of them that I'm dead." The ghost saw no point in being delicate and decided to be blunt. The young Potter swallowed, his green eyes widening.
"I don't intend to use them !" He looked offended.
He moved to stand in front of the boy. "Well, you said that now. I used them and here I am, I'm not sure your parents would be very happy to see what kind of reading you're doing here".
"They can't be that bad," the boy muttered.
"Fancy hearing that from Harry Potter's son," he snorted at the boy who glared at him.
"Dad doesn't talk about dark magic, he doesn't talk about the war at all, he just tells us not to use it or read about it or even talk about it."
The ghost sighed, "Long story short, a boy split his soul with very dark magic, using murder to do it, and put the piece into objects to anchor it, and then slowly became an unstable madman who killed your grandparents, made your father another anchor for his decaying soul, and killed half the wizarding world for absolutely nothing. I suppose Potter is still a bit traumatised."
Albus frowned at him, "I didn't know that, well, they explained a bit about Voldemort and the war and why he's famous, but not the soul part... That's gruesome."
“Quite”
"Why did he do it? You were with him? That's why you said you died because of dark magic?" Potter looked at him with piercing green eyes, he looked a little naive and innocent.
"Me? Oh no, I wasn't with him."
"Oh cool, so why did you use it then?"
The ghost blinked and tilted his head. "Simply because I was Voldemort. Hi ! Nice to meet you. Call me Tom" There was silence then the boy scrambled to his feet and walked as far away from him in the room as humanly possible.
"WHAT?"
"Do you realise that I am a ghost ? I couldn't hurt you even if I wanted to. Because let me be clear, my soul is quite complete now, which means I am more mentally stable as a ghost than I was as a man of blood and flesh. How ironic," Tom tried to touch the couch but, well, his hand just went right through it, he sighed. The fabric looked so soft.
"B...But, how? Why? What! Merlin!" Tom just hoped the boy wasn't about to have a heart attack. He'd already killed Harry Potter's parents, let's not add his son to the list.
"For the 'how', well I was afraid of dying so I refused to cross to the other side, for the 'why', well I just said it, as for the 'what', I have no idea how to answer that," He said matter-of-factly.
"Okay, okay, okay, you're actually the Dark Lord Voldemort, fine, I'm fine..."
Tom shook his head, "No, Voldemort is gone, I'm Tom Riddle, Voldemort was... I don't know what he was, some kind of empty shell, stuck in the same loop, spouting the same nonsense, he was quite nonsensical".
The boy nodded seriously and took a step closer, "Tom Riddle, okay, okay, so the person you were before Voldemort, that's why you're so young.
"Yes, I made my first Horcrux when I was sixteen, which means I wasn't quite myself at that age already, but it's really after the third one that I definitely lost it.
"How come no one ever saw you, I mean the professors, the headmistress?"
Tom's lips twitched, "Destroying my soul didn't just affect my psyche, Potter, it affected my body too, Voldemort barely looked human. Besides, very few people know that Tom Riddle and Voldemort are one and the same."
Albus nodded thoughtfully, "And I'm the first one you talk to? Why?"
He grinned, "Because you worry me, your fascination with the Dark Arts is not unlike my own, and it didn't end well, as you know".
"Wow," Albus looked scared now, "OK, I'll stop."
They stared at each other for a while and Tom hesitated to say anything, "You can still talk to me if you need to. To keep a respectable distance between you and the darkest form of magic. If that's all right with you, of course."
The boy blinked, "Yeah, yeah, why not, that would help".
From now on, a strange kind of friendship developed between Harry Potter's second son, Albus Potter, and the damned complete soul of Tom Riddle. Tom kept an eye on the boy and even encouraged him to apologise to his friends and explain why he had become so distant. This time they were in the abandoned classroom of the Thor floor and Albus was brewing a potion when Tom brought up the subject.
"Why should I explain it to them? They would just laugh".
Perhaps becoming a therapist in his damned half-second life was Tom's punishment. "I tend to think that if I'd had friends, real friends, maybe I wouldn't have turned out so bad. Maybe" He wasn't really sure, but little Potter had plenty of friends and family to love and support him.
Potter looked at him, "You know I'm not exactly like you, right?" He carefully added some mandrake roots to his potion.
Tom looked at his ghostly nails and simply said, "Of course you're not, despite my many faults, I'm still a genius." He received a blank look from Albus.
Tom continues to watch over the young Potter, knowing the addictive nature of Dark Magic and not wanting to see anyone fall for it as badly as he had. The consequences are rather unpleasant for all parties involved.