Ralsei or bust is still entirely possible if we assume Kris' soul really can allow a darkener to go to the light world like Spamton thinks
>Be in the dark world
>Kris removes the soul and shoves it into Ralsei
>Actually just make the soul enter him itself so Ralsei doesn't moan everytime Kris sticks his hand into his chest
>We don't know what the max amount of time Kris can spend without his time, but evidently it's kind of awhile if he's able to lung around, carry a kid his age, and gaslight Noelle a bit in one night
>Who's to say the festival is too long?
>No dark world magic, so the soul inside of Ralsei should be mostly harmless as long as Noelle is kept far away
>You can't really make Kris murder anyone in Castle Town, so there's no reason it would change with Ralsei
>Eventually Ralsei can rip the soul out himself as soon as they get back into the dark world
>If Kris is able to constantly hide stuff from us while being actively possessed, then Ralsei damn sure is
The only possible fuckups are Noelle recognizing the soul if she's been mindbroke hard enough or Kris collapsing in the middle of the festival.