Kris originally having a cyan-colored soul before the Player’s arrival is something I genuinely havent’s seen theorized since Chapter 1. And back then it relied a lot on flimsy evidence that included blue hearts next to Jockington-themed locker graffiti. But now with the anniversary stream, we have:
Musical leitmotifs only featured in Deltarune being present in the anniversary stream Ruins
The buildings of these Ruins being shaped exactly like the ones in Deltarunes intro
The cyan soul’s signature toy knife being moved from the balcony into this new area
Kris having a bandage as a default armor and a knife they keep on them at all times, both being items used in the cyan soul section of the Omega Flowey fight
Kris’s skin in the Dark World being inexplicably cyan
So, like, Kris being the second fallen human and cyan soul might be back.
Right now, it seems like the theory’s biggest hurdle to overcome is the fact that maybe it’d be kinda silly to have Kris be a perfect combination of Frisk and Chara right down to their name, only for their true Undertale counterpart to be the second fallen human, a character completely separate from either of them.