HP:[" the Illithid Inquisition"]

Not exactly. It answered. Something that small doesn't have much of a mind to speak of, let alone any thoughts or personality. I would say that I'm what the psychic essence of that tadpole might have made if it had been left to eat and replace your mind. But that isn't entirely true either. Really I'm the Illithid half of your thoughts.

"If that's the case why did you help me escape?" Harry demanded to know. He didn't like the idea of something so foreign being in his brain. "You might not be able to control my body but you could send out your thoughts. You could've told the Ulitharid that I was still alive, instead you helped me trick him."

The cold answer is that doing that would've killed me. The voice answered simply. In more ways than one at that. Firstly I don't think we have enough body mass to undergo a proper ceremorphosis so stepping into one of those pods would've killed us outright. Second Illithids believe that any amount of surviving personality from the past host is a disease, one terrible enough to justify digging out parts of their brain to destroy the part that wasn't properly overwritten. The Elder Brain would never let an Ulitharid fully mature with such a defective brain. They're probably already planning to have us killed once we've gotten this world's subversion properly underway. Thirdly, even if we fully underwent a proper and effective ceremorphosis I doubt my personality would be the one to come out intact. Your mind is very resilient at any attempt to subvert it so your personality is probably going to be dominant in here for as long as we live. And if anything happened to this mind powerful enough to destroy your personality it would probably destroy mine as well and replace us both with a proper Illithid. Finally I don't want to be an Illithid.

When that tadpole fused with your brain, your magic overrode whatever psychic essence it possessed and replaced it with a near copy of your own soul. I'm no longer whatever that tadpole was going to be. I think I'm what you might have been if you had grown up in an Illithid colony. I'm not a human mind. But I'm not an Illithid mind either. I'm something unique to you. And I don't mind that.

"How did that happen though?" Harry wondered. "I don't remember trying to do that, I don't remember doing anything when that tadpole entered my eye other than trying to squirm away from it and then passing out."

I'm not certain, but I doubt it was anything you chose to do. The voice explained. If I had to guess, well. You know that other part of your mind you can't access?

"I do." Harry confirmed.

I think that was created when someone tried to insert part of their own soul into yours. The voice explained.

"What? When did that happen? Why?" Harry asked, startled by the idea that there was something else in his head.

I don't know when it happened. Long long ago I think. As for why, my best guess is that it's trying to anchor the rest of its soul to this plane of existence. I was awake for a few days before you regained control of your body and I asked the Elder Brain about souls and why someone might try and put them into something else. It said sometimes a powerful kind of wizard called a lich can put their souls into special containers called phylactery which allows them to remotely control their bodies with magic even after they've rotted away until their nothing but bones. So someone might have tried something similar with you.

"That makes some sense actually." Harry agreed. "Lord Voldemort was afraid of death according to Professor Dumbledore. When his curse reflected off of me he might've tried something desperate like putting a part of himself in me to try and survive."

Harry thought about this for a few seconds and then shuddered in revulsion. "So I've got a part of my parents' killer inside my head? I hate that. Wait, does this mean I'm what's keeping the dark Lord from passing on? That's even worse."

It won't be an issue for much longer I think. The voice reassured him. I think your soul is trying to digest that part of yourself. To break it down and make it into a part of you without changing your own soul too much. Another decade or so and he'll be gone completely. And in the meantime I think you've learned a magical language from it and picked up a natural resistance to and talent for using curses. Which may prove useful when we go to kill the Elder Brain.

"I don't like the thought of absorbing anything from Voldemort. I don't care how useful it might be." Harry insisted. "Does this mean I'm also digesting you?"

Kind of. Voice answered which seemed to be its answer for most things. I'm not a soul. Illithids don't really have souls. I'm just a bundle of psychic energy so I was just overwritten and made into a part of your own consciousness. A semi independent part mind you, but still a part of you. By the time we've undergone full Ceremorphosis you and I will probably have synthesized together, or you'll have grown up enough to fully incorporate me into yourself.

"That makes it sound like I'll have killed you." Harry noted, not really liking the sound of that. He hadn't asked for a voice inside his head, but he couldn't deny the guy was helpful and he didn't want anything bad to happen to him.

From one point of view maybe. The voice answered a little nonchalantly, From another I will live on as part of you. I've got no problem with that. It's what happens to all Illithids eventually. All our minds are eventually absorbed into the Elder Brain, joined together into a single collective consciousness. A true and absolute unity. It's the whole reason why we even have Elder Brains in the first place. And Ulitharids too for that matter.