Does christian holy water affects Japanese demons?

It depends on the rules of your world. If One God is the only God, and is providing the power of the holy water, AND, if the Japanese demons are simply branch offices/entities of Hell, Inc., then perhaps it could. But If Christian magic only works on Christian beings then no, it wouldn't. Japanese demons seem to be more mutants with super-strength rather than Christian-hell-inspired demons.

No. Actually, when Christianity was banned in Japan, some Christians were rounded up and drowned in holy Japanese water.

Neither demons nor holy water are real.

No Japanese demons fear noise more chimes to firecrackers. you also need a demon wall behind your door as they like to travel in a strait line. That keeps them from entering the home.

Neither demons nor holy water are in the world today.

Mythological demons in Buddhism aren't always considered evil. They're looked at in shades of gray, instead of Christianity's good vs bad. Christian and Western mythology doesn't translate to Japanese mythology.

If you ever encounter a kappa, just bow. It's so polite it has to bow too and then its magic water spills out of its head and it has to leave to refill.

There is no such thing as "Holy " Water. and Demons are demons.

It will make them wet.

Both are imaginary . So , no .