Why didn't Fuyumi and Hydra Bell fuse like their mothers did?


From what I understand, When two opposite individuals (one from the human
world and one from the demon world) touch each other, they are fused together
to create one new individual that is made of the two of them.

So if Fuyumi and Hydra Bell are both the daughters of Nyen (Nene), why they
didn't fuse when they touched each other?




The straightforward answer to your question is that Fuyumi and Bell aren't
doppelgangers ("opposites") for each other, and so there's no reason one
should expect that they would fuse with each other.

Sure, their _mothers_ were doppelgangers, but that doesn't mean that their
children - Fuyumi and Bell - should also be. For one thing, they don't look
very much like one another, whereas their mothers (pre-fusion) totally did:

![](https://i.stack.imgur.com/tVQKvl.jpg)

