wiki says nereids are sea nymphs from greek mythology. says they're very friendly and help sailors escape from sea storms, so im not sure if they would be the succubus version of a mermaid. besides, it looks too nice, rather than seductive
from what I know(I just guess by what I can understand)... it is not a kind monster... 1. it may be able to turn girl into monster(or?).(how? I don't know, but I believe that it is something like human girl drown into the water, then Poseidon or whoever he is gives that girl power and turns her into that kind of monster) 2. she is seductive.(maybe she seduces man like succubus... who knows?)
Somehow... I hate myself for knowing Mandarin but not Japanese...
