Disclaimer: I own nothing, J.K. Rowling does.
I remember being a part of a broken soul. Then at the end of October of the year 1980, I was ripped from that soul and flew to the forehead of the babe the soul came to kill. I kept trying to possess the baby, but no matter how hard I tried the babe's magic kept me back. I gained the ability to see through the child's eyes and feel its' emotions through those attempts.
The child's relatives scared the child beyond comprehension and that brought me great pleasure for pain and fear were the only emotions I knew and I liked to make others feel them. The relatives hated and loathed the boy (two more emotions I knew of). They threw the child in the cupboard under the stairs and left him there for days on end, only occasionally throwing a bottle to the boy.
The boy became known as freak and boy because that is all the relatives called the boy. He did every household chore, from cooking, to painting, to cleaning. When gardening became a chore for the boy, he discovered a small garden snake and, much to my surprise was able to speak to the snake and understand it. The boy named the snake Athena and he felt an emotion I didn't know off for the snake, the same emotion he felt for the spiders from the cupboard under the stairs. This emotion baffled my mind because the boy didn't know what the emotion was either, he just felt it.
Years went by and the boy became known as Harry when he went to primary school. I could tell he was an intelligent child, but he was held back by his relatives. He wasn't allowed to do better than the pig that was his cousin. Harry continued to feel that emotion for Athena and the spiders, but he came to feel it for playing on the swings at the playground at his school and simply walking through the park.
The day his Hogwarts letter came was a day of confusion and fear for the boy. He was confused as to what the letter said, where it came from, and how his relatives acted because of it. He feared the reactions of his relatives. The fear and confusion grew as the letters kept on coming. The relatives became crazy as time went on and relocated the boy and themselves to a tiny island that was little more than a shack on a rack.
The oaf of a giant, Hagrid, was an idiot. He didn't explain anything of the wizarding world to the boy and then didn't tell the boy how to get on the train itself. Only good he did was curse the whale of a cousin. The boy named the owl he got Hedwig and grew to feel that emotion that stilled eluded me for the bird.
The boy's first year flew by with him growing to feel that emotion for the Weasley boy, the mudblood girl, quidditch, and Hagrid. He hated the Malfoy boy, Quirell, the soul I broke off from, and Snape. Stupid Dumbledore for keeping the stone and mirror in a school and with such measly protections that a group of first years could get through them.
I learned what the emotion was in Harry's second year. The Weasley matriarch loved the boy as if he were her own child and the boy felt the same for the women. She told the boy she loved him and fussed over him when he seemed amazed at that.
The years went by with me learning more about how to love from the boy. He was so innocent in how to love something, but he had no idea what it was like to be loved. I learned more about how to feel from Harry than in my whole long life. I grew to love Harry because of this. I knew everything about him and yet he didn't even know I existed. I hated that the soul I broke off from was set on killing Harry.
When Harry and his friends went on the hunt to destroy the horcruxes, I wasn't enraged, I agreed with the sentiment that Voldemort had to die. He was endangering the life of the one I loved. I knew that this would me I would have to die, but I would choose Harry's life over mine anytime.
As Harry walked to his death in the Forbidden Forest because he thought that was the only to destroy me, I was terrified. I didn't know if I would be truly killed or if only Harry's soul would be sent to the afterlife. He told Voldemort to kill him and I could only watch helplessly as the green of the Avada Kadavra sped toward Harry and I.
I panicked in that moment and used all the power I had to envelope Harry's soul with my own. I was then lost to blackness as the light hit us.
I woke in a light filled King's Cross Station where I met Death. He told me that my actions saved Harry, that Harry stilled continued to live and fight to kill Voldemort once and for all. He said that because I learned to love and sacrificed myself for Harry I would be allowed to go on to the afterlife without waiting for the rest of the soul I came from. I became my own soul/person by learning to love. I boarded the train to the afterlife to wait patiently for Harry to join me, his parents, and everyone else after he lived a long prosperous life.