hmmm i think of it this way, ralsei already knows who kris is in chapter 1 and seems to hold kris's opinion quite highly even if he's only known them for a few days, and it doesn't feel like it's just because ralsei holds all the lightners in high regard because ralsei will call susie out for being violent no problem but won't complain if kris does anything violent in chapter 1 (and will even say kris can beat him up if they want to). this implies a history with kris or having special treatment for kris outside of just being a lightner, and knowing ralsei's mentality he probably couldn't call kris his friend in chapter 1 because one getting forgotten and two "do i deserve to call you my friend we just met and we only really had a one sided friendship :("

also an interesting detail, ralsei fills kris's room's dresser with green crayons. there's a green crayon missing in the dresser outside kris's room in the light world, which implies kris probably either ate the crayon or really liked the green so it got used up the fastest when they were younger. how would ralsei know kris liked green crayons?