The Dark Arena
Entertainment Gone Awry
Four years into his stay with the Dursleys, Harry suddenly vanishes from Private Drive. No one in the Wizarding World has a clue where he is or what happened to him or if he's even still alive.
Year 1:
With Harry's absence, Draco quickly establishes himself as the top dog in his Hogwarts year thanks to his father's abundant wealth and social power. On Halloween, Hermione is caught by surprise by the troll in the bathroom. Because she'd left her wand in her dormitory, she was powerless to defend herself from the troll. Snape, McGonagall, and Quirrell arrived too late to stop the troll, they only had enough time to listen to Hermione's last words (that she wished she could've made at least one friend before she died). Draco was disappointed that he never got the chance to show her that he was far superior to her in all things before she died. Ron, though initially sad and remorseful, quickly became absolutely ecstatic that she no longer was in class anymore and couldn't preach to him about things she (he) didn't understand. Ron's coarse and blatantly happy behavior to Hermione's death caused many of the Gryffindors, and eventually the rest of the school, to take a deep disliking to him.
During the First Year, Dumbledore had been forced to hide the Philosopher's Stone to protect for his friend when it was discovered that someone was seeking to steal it. Unfortunately, at the end of the year, the Stone was still stolen by his new Defense teacher Quirrell. Voldemort made six Horcruxes but only the one accidentally created in Harry Potter saved Voldemort's life. When Voldemort drank the Elixir of Life, his fragmented soul was reassembled because one soul magic (Horcruxes) cannot work with another one (Elixir of Life).
Year 2:
Lucius tries to plant Riddle's diary Horcrux in Ginny's things so that the Dark object would start running amok at Hogwarts. But because of Voldemort's consumption of the Elixir, the diary Horcrux no longer was a Dark Object. Thus the Chamber of Secrets never opened, despite Ginny's constant use of the book.
Draco turns his attentions to making Lockhart's life miserable, something that he accomplished with overwhelming success. Draco also uses his pocket money to buy his way onto the Slytherin Quidditch team. Thanks to the Nimbus 2001 brooms, they easily dominate the entire season and win the House Cup by a landslide of 800+ extra points. Because of these victories, Draco's status in Slytherin House is further elevated.
Year 3:
With the escape of Sirius Black and twenty other captured Death Eaters from Azkaban, Dementors are sent to the guard Hogwarts. Dumbledore hastily calls the Order of the Phoenix together and they begin active recruitment and planning to fight in another war. Predicting that Voldemort will desire to see the contents of the prophecy, Dumbledore begins stationing watchmen to protect it. And while Voldemort is interested in it, he's far more busy acquiring rare and powerful magical artifacts to increase his fighting power and abilities. He's already gotten an ancient Egyptian scepter that can transmute anything by using Alchemy, a Mithrill sword (believed to be Excalibur), the Greek golden fleece that can heal any wound, and he is currently searching for the Elder Wand.
At Hogwarts, Draco is practically living the life he's always dreamed he would. He's got everything he'd ever wanted; the respect of his House, the fear of the rest of the school, the wealth to buy whatever he wants, the magical skill to be a difficult opponent for nearly all of his year-mates, and the political savvy to get his way in nearly any argument he gets into. And yet, he's constantly finding himself bored and yearning for something…more. For all of his accomplishments, the lack of a serious rival to focus on and test his mettle against is causing him to become increasingly angry, not that he's aware of what's causing him this trouble. Draco and the other Slytherins took great delight in getting Remus fired from Hogwarts when it was 'discovered' (told to them by Snape) that he was a werewolf.
Summer before Year 4:
As summer vacation began, Draco Malfoy and some of his friends get taken to the old underground Roman coliseum (nowadays called the Dark Arena) by his father. The Dark Arena had been created by the Roman wizards 2,000 years earlier. While they watch the fights take place, they hear rumors of an old champion's return to the Arena. Draco, believing he could use his 'influence' to get the results he wanted, decided to make a large bet against this champion while paying some of the officials to rig the fight to his favor. The champion was the heavily favored fighter and Draco would've made a lot of money if he lost the fight. Draco, his friends, and his father were all greatly surprised to learn that the champion was actually a mere teenager no older than Draco himself. Despite the fight actually already being heavily rigged against him, the champion still won the fight by a landslide (and without even using any magic). The champion was Harry Potter.
Intrigued by the champion, Draco and company decided to pay a visit to the boy to learn more about him. The boy was so covered in bandages, ragged clothes and armor, and old battle scars that none of them could clearly identify who he was. Even his eyes were strange; one was a dull green and the other like golden feline. The Slytherins are happy to learn that Harry's current master is a man who owes them a tremendous amount of debt. At first, Draco tried to talk his father into purchasing Harry but Lucius decided that he didn't want to buy the slave after all. Draco and company leave to return to watch the other fights taking place.
Later that night, Harry receives some unexpected help. A slave revolt takes place in the arena containment cells and several slaves escape, Harry included. Harry was able to use the guard's key to unlock his shackles. Unrestrained, he steals two swords and fights his way to freedom, with a small group of slaves behind him. Harry singlehandedly kills more than thirty guards as he was heading towards the surface. Once free of the Dark Arena's anti-Apparation field, many of the slaves teleport to freedom and go into hiding.
Harry waits to cover their retreats by sacrificing himself. It is as he's fleeing himself, he gets hit by a powerful Memory Charm, leaving him with no memories and only ingrained fighting instincts. Harry awakens in a park wearing rags, rusty armor, a pair of bloodied swords, and a manacle on his left wrist with the name 'Harry J. P.' He decides to use the name until he figures out who he was, where he was, and what had happened to him.
Year 4
Following his instincts, Harry goes to where he senses a great power. He finds himself in some kind of street filled with many magical things. As he's browsing through the street, he gets attacked by a pair of strange robed thugs. Harry kills them without hesitation or remorse, reacting solely on instinct. He pilfers their bodies, taking money, clothes, whatever magical objects they had, and dumped them in a side alley to be devoured by carrion eaters.
Deciding that he didn't like the feel of the atmosphere in this street, he heads to where he senses a more free power and emerges onto a completely different street. Liking this street more, he wanders about, finding a place to at night in a side alley, and does some research in the book store for recent events and history. He learns of Voldemort's return, the missing BWL, the coming Triwizard Tournament, Gringotts, and Hogwarts. With nothing better to do and reluctantly interested in seeing what a normal kid does, Harry decides to go see this magic school for himself.
But as he's looking for directions to get to Hogwarts, he draws some unwanted attention by some junior DE who were looking to cause trouble to inflate their egos. They chose to pick a fight with Harry because, despite the robes he wore, it was quite obvious he wasn't a DE himself. When they start to get violent, Harry attacks and incapacitates them, critically injuring them in the process. The scuffle was observed by quite a few bystanders who were shocked at his fearlessness and combat skills to publically fight against Voldemort's supporters. Unconcerned with his sudden rise to infamy, Harry merely asks for directions to Hogwarts but no one's willing to help him so he sets off on his own, following his instincts again.
Harry's Past
When he was four years old, a strange man had come to his relatives' house and paid them a tremendous amount of money to purchase Harry from them, effectively making Harry his slave. The man who took Harry began immediately training him to become a merciless killer who was highly proficient in magical and non-magical combat (his favored style is using two swords). When Harry turned ten, the man entered him into his first fight in the coliseums, which he barely won.
Harry would spend the next four years traveling all over Europe, fighting in many different coliseums like a gladiator for a crowd of Dark wizards' and creatures' amusement while filling the pockets of his owners (his owners had a tendency of winding up dead because other gamblers or competitors would kill them to claim ownership of him).
Though he fought ruthlessly and savagely as a way to vent his pent up rage, the one thing Harry desired above all else was his freedom. But he was quite literally bound in shackles that prevented his escape, despite how magically powerful he had become over the years. The shackles identified him as a slave and who his current owner was.
The only things that Harry had to truly call his own were his power and his special left eye. His golden left eye was a transplanted gift to him from one of his previous owners after he fought and managed to kill a magically-powerful Liger while in Istanbul. Unknown to anyone but himself, the Liger eye gives him the unique magical ability to foresee the flow of battle and allows him to react/counter it as he sees fit. The Liger eye also gives him a somewhat limited ability to see when someone near him was under a curse's effect (he usually saw the Imperius due his common crowd of Dark wizard owners). This is the unknown reason of why Ligers are considered to be among of the most dangerous of magical creatures, just under dragons.