Haria did not always have a portal to the Warrens, nor did many worlds; a few of them always did, but never enough to populate the warrens to the extent that they are now. Several years ago, 7 meteors crashed on Haria, depositing little toddlers, with some amazing psychic abilities. Obviously they must be magic to survive a meteor crash. So they were locked up, in order to protect the world from them. They grew up in the prison system, and on a fateful day, received magic technological artifacts that Proxxy had built, and started playing a game.
Oric managed to almost single-handedly win this game. Which as you know by now is Sburb. He had converted the entire Rift into grist by the time the next player entered the chain; preventing any meteors from crashing into Haria but the ones he and his paradox-clone-"Siblings" rode in on. He wiped out the black team entirely (including Jack, his session had no Outcasts to guide his group), and was horrified each time Cain ate one of the Sibling's time-clones. Eventually, they actually won; they had actually saved Haria, defeated all the enemies, and were free to do with their universe as they pleased. Oric had known that he was fated to win from the start, it had been tattooed to his chest; and felt like winning left him empty.
Like a chicken raised in captivity and released to the wild, he felt lost without a goal. He was raised in a prison literally, and was prisoner to the game his whole life... being "free" was foreign to him, and he didn't like it. So in one of the 7 craters, he built a massive portal. He announced to the kingdom that for their safety, he was returning to captivity, and left the entire universe through the portal. He found himself in the Warrens, where the natives had put themselves into suspended animation for the most part, and defeated those who remained, either slaying them or subverting them. His portal had a side effect, though, and it opened the Warrens to more universes, and more universes. Denizens started pouring in, and he had his hands full managing them. He sacrificed most of his sweet loot and power to build OricSoft, a massive computer that would separate the soul from incoming travelers and make them easier to manage by completely cataloging them. He locked up Cain, who was becoming a problem, and assigned his other siblings to maintaining the Warrens. Back in the Skaia 'verse, though, the Sburb programming recognized that Oric was subverting his destiny of being a free man by locking himself up and becoming the Warden of the prison he now occupied. It sent out an agent, through a portal into Haria, and then through the portal into the Warrens. This agent (the village Chief, I think) sabotaged two of the Siblings, who had been augmented while they were players of Sburb, and turned them against Oric, directing them to free him from the prison by any means, including death if need be. These were the Target and
?, who we know as Oric and Riltia. Oric realized that should the Target ever succeed at removing him from the Warrens, he would be lost again, and set to stopping his Sibling from removing him from the Warrens. He killed his siblings, then resurected them in hopes that the agent's influence would be defeated. It worked, mostly, on
?, but not on the Target. They lost their identities, but the Target still had it in his mind to remove Oric from the Warrens, and
? was easily impressionable and was swayed by the Target to join up. Oric defeated them again... and again... and again... until it sort of turned into a grand game for Oric, with challenge and danger and varying but repeating situations. Oric wants the Target dead so that he can save the Target from the agent's influence.