Hey Kelikoi! I know a bit of Japanese so I know how to politely ask for their permission. 95% of the time even if they are in a hurry they will say yes. I actually think it helps being a "gaijin" cuz they do understand my question however they know i cant really speak japanese so they know they cant counter attack with a reason as to why I cant take their photo :P
Ive seen your pics as well, great batch (70-200 is a beast) ! So since we both been there you know how shy and polite they are, I guess its just difficult for them to say no