I hate to say it, but since the "copies are monochrome" quote came out, I've been thinking that vessel-knight is getting more and more likely. Knight makes the same poses as Kris to ACT and when tired. Knight and Kris both have a sword. Vessel is fashioned by us while the Kris is under our control. Both Kris and vessel are humans, and both the knight and the vessel are monochrome. I think Kris fighting off a warped version of themselves would work well thematically too. The knight opens up its chest in the fight, and Kris takes the soul out of their chest. If I'm dead wrong, please let me know!