The single scene I believe nailed down Kris's entire trajectory, that explained the most about them as a character, has to be their chapter four piano concert:
We, as the player, have no input in this scene at all. If you try to play the long sequence right, they'll just mess it up, prompting the dialogue anyway. There's no command from us that they twist in order to be "allowed" to play, no nudge from us in the right direction- they just snatch control, because Susie wants to hear them.
This is such a complete stab through the gut, not just because of their passion and the fluid animation and sheer expressiveness, but because Kris can just do that! It isn't that they physically can't play piano with the soul in the driver's seat, they just won't, until Susie empowers them to. No matter how badly they want the freedom to express themselves on their own terms, they restrain themselves. They let us take the reins and try to just submit, and they can't keep it up.
The interpretation this strikes me with, coupled with their "knighting" and their "promise" to the mysterious caller and their unspecified egg trauma... We know they know how we work, and that their plans with us are premeditated and calculated, at the behest of (maybe multiple) adults who have significant power over them. At least the Mayor is directing them to let themselves be turned into a vessel. We know this would have to have started before they went to the first Dark World, when Susie was still a bully, Noelle estranged and Ralsei not even in the picture.
We know that by the opening of the third fountain, by the time they're spinning prompts to get into banter with Susie and blocking us from being mean to Ralsei and drawing messages on windows and sneaking in as much of themselves into their relationships as possible, they've been turning themselves into our tool to be ultimately pitted against the group since day one. That no matter how much they can be coaxed out, at the end of the day, they have to be shoved back in their place, if not by us, by the Knight/mayor/etc who've facilitated this entire thing. That their choices don't matter.
Evil-Kris officially out, Deeply-Conflicted-Kris officially in. Of course earlier Kris tries to keep themselves closed off from the Extended Fun Gang- no matter how much they adventure together, how much they grow to like their company, Kris will inevitably, in their eyes, have to betray them. Because they made their choice before the story could even begin. Because they promised.
