*shrugs* Like I've been saying... my one complaint is that things like this are never officially and fully explained in the game itself.
You do have some very good points, Ganheim, though I need to rewatch that scene with Skeith since I remember it more as Skeith trying to convince Haseo that his friends are a pain and then saying "You don't need me anymore." rather than just saying "I'm leaving." But like Zelkova said, the Xth form is powered by Skeith. In other words, I've always thought of that scene is more symbolic than actually "happening" (It's basically a dream) in the sense that both of Haseo's "sides" so to speak, have finally come together as a single entity. His jerk-like badass angry side, and his caring and sympathetic good side.