Rerir is still from Khaenri'ah, yea. But since I assume only pure blood Khaenri'ahns got star-shaped pupils and also they were the ones that got cursed with immortality and decay, he's still immortal! Just not corrupted. About his motivation… He's still a former assassin here, but he failed both to follow Tholindis and to get the curse of the Abyss, so he kinda just? Fled the country after the other Sinners got corrupted??
oohhhh the lämp, I just found a cool one and I also think that mayhaps he stole it long time ago to navigate thru the snow
His motivation to move to Nod Krai is also still fueled by the fact that it has some special Moon Lore^tm and he he wants to find a way to figure out what exactly happened to Tholindis and all that moon lore stuff in general. Being a ratnik is also a good alibi for being an antisocial freak and for roaming everywhere? I mean I doubt he'd want to go to the Scions with their cult thing 500 years ago, lmao
And I think Flins got corrupted while sleeping underground, during the Wild Hunt's attack that awakened the original Flins. But since this time they had Rerir fighting there, he just kinda… looked at that immortal 7ft+ tall ruthless man and thought "woah…"
And then his original sad thoughts and grudges became 10 times more intense - thank u Abyss corruption - so Flins became obsessed with like, finding a way to stop the world from changing? Like oooohhhh I gotta help people realize the original Three Moons are dead and they need to resurrect them and also Heavenly Principles Suck Ass. But since it's Abyss he got it all backwards and decided that Colombina is a fraud and ain't ready and should be killed so the new better Moon Goddess can be born
Compared to original Rerir, abyss-corrupted Flins is more like mythically accurate fae folk, chaotic neutral (borderline evil) trickster critter??
Also instead of the heart incident Flins loses his wings while being corrupted by the Abyss and then spends a good while trying to find his lantern first to regain his physical form, and then - his wings. Like. Who stole them. So he went around and killed a bunch of butterflies and then saw Rerir holding a very peculiar butterfly and like. Oh. That's mine. Give it back. And then hooray obsession
Rerir thinks he's pretty like a butterfly but he loves butterflies trapped under the glass, so… Like idk how morally wrong or right they both are, I think in the end they both are creepy freaks either way.