Responses

well tecnically is legal only in that city

Shibuya is a ward of Tokyo. I'm not really sure how that exactly translates to the law. You can get married there, now, and same-sex marriage is recognized in that area, yet the rest of Japan does not. It's probably like stepping into a state that doesn't recognize same-sex mairrage. Over 200k live in that area.
Especially poignant with same-sex marriage recently granted in Shibuya.