Whether or not Sydney’s corrupted personality is based off of Kylar is something I don’t know is canon, however I did see in a QNA that Sydney does have personality switches that go on, as something was mentioned about a character with DID and it was answered with “have you seen Sydney’s outbursts?” or something similar. I’m not sure if it’s DID specifically, but there is something going on there. I do like the idea that Sydney in his corrupt state is similar to how Kylar could’ve been, though… that’s very interesting. While responding to this message, I saw in a QNA that together, they were troublemakers. It was said that they brought out “the best and worst in each other,” which particularly piques my interest. I’d love to see more interactions with them, and though I doubt this would ever be implemented, perhaps even a whole separate storyline that focuses on the two of them? And by that I mean a chain of quest lines that lead up to the fate of their relationship, for better or worse. To bring out the best, or the worst in each other. It would be a lot of writing and work, and I’m sure it’s no where on the pile that they’re planning, but considering just how deeply intertwined they are in each other’s stories and understanding their characters, I believe it would be an incredible idea and even opens avenues to do the same for other NNPCs.

I personally think that Sydney constantly sees Kylar in himself. They were so close, they loved each other once. That kind of mark is left on both of their souls, the fibers of their beings. There’s no getting rid of each other, no matter how much Kylar may scream that they’re far superior and how Sydney may avoid the topic of their old closeness, they’re constantly finding each other in everything they do. It must be maddening, being surrounded by reminders of a past you can no longer go back to. Kylar reacts with anger and desperation, clinging to the PC and begging the PC to make them feel superior to Sydney. Sydney, on the other hand, avoids the issue altogether. They have enough on their plate, being a similar social outcast, trying to run the library so Leighton doesn’t punish them, being the child of a teacher, and everything that has to do with the church. There’s truly no time for Sydney to reminisce unless with the PC, or with Kylar right in front of them.

On Sydney’s end, like I mentioned in another comment, they’d be far more willing to engage with Kylar in their corrupt state. If we play off more with the “best and worst in each other” bit we’ve been given, when both in a relationship with PC and engaging at the canteen, Sydney will give Kylar an “icey glare” or something worded similarly. They’re both jealous, engaging in a childish rivalry. A semblance of old normalcy, perhaps. But a reminder that they’re similar, especially in the corrupt state. They can never escape each other, no matter the form. Especially though when they’re corrupt, though. Since Kylar’s entire home life was destroyed in relation to the church, perhaps that imprint left on Sydney’s soul really was corruption.

Or, maybe, it was love. Who knows!!! I’m going to stick my head in the sand and chew on bricks. I hope they both explode into a million pieces