I'm personally all for it being set in Japan or better yet, if you want to go by the ambiguous route, a city set "somewhere in Asia" and limiting it to Asian mythology only. I've had my fair share of Western mythology rps which are far easier to come by (most general "fantasy" rps have dragons, elves, fairies, vampires and the like) so it'd be a nice change to have the setting be more Asia-focused and deal with creatures and concepts that aren't used as often (for this, Asian mythology would work better than just Japan's, so I root for that). I also feel like it would give the rp a more cohesive feel if it was centered around one country/continent instead of being scattered around all over the globe, which could get messy fast. That, and when the options are more limited, people might need to step outside their comfort zones and study creatures and myths they aren't already familiar with. Research is fun. Your character could still be from a Western country if you really want, with the added bonus of them having to familiarize themselves with the mythology and lore of the city they now live in. Character development ahoy?

tl;dr: I want something Asia-centered for once plz.