the Ralsei tea being nothing at all does align with the weird Ralsei "down" sprite - it being literally just Ralsei's clothes and no body at all. Then there's the whole thing about him knowing so much about how the darkner world works yet seemingly never learning the basics of friendship (which you'd think you'd learn when becoming a healer and acquiring so much knowledge about the world).

In the Light world, characters from dark world become the items related to them.
Ralsei is the knife.
He is from the Main Fountain, comes from the same way as kris and susie, etc.