I mean, personally I think it's stupid, but eh.

I also don't really understand the decision... as I really don't think Yokai Watch is remotely popular with the majority of players. YW is a (young) children's anime and game. It really doesn't have that many fans over elementary school age (and I say this as someone who lives and works in Japan). Even among adult anime fans, YW is not popular. So... in that sense I don't get it.

And I do understand OP's feelings about it being immersion breaking. Sure, you can claim the other "silly" stuff in the game does the same thing, but it really doesn't. An established, famous brand suddenly appearing is not the same as seeing someone dressed in a random silly outfit. I mean, wouldn't you feel it was immersion breaking if McDonalds themed stuff was put in the game?

If you don't have a problem with it that's fine, but I don't think OP's feelings are unreasonable.