Yeah i think ralsei is NOT a darkner. Flowery has some dialogue that points towards the idea ralsei is pretending to be something he's not. And honestly there isn't a single object that makes sense for him. I think he might be more similar to a titan or darkguy.

I beveroni thinked about it, mante ur right

I dont thinl ralsei is an abject bcuZ hes made from pure darkness

twin this drawing is so peak

The idea of asriel just shedding fur around town would be disgusting but it may be a piece of fur on kris after a goodbye hug from asriel