I don't live in Tokyo. I'm in Osaka. 
As far as I know, Nostr developer events are not held very often in Japan. There were online study sessions last year, but they haven't been held for a while. 
By the way, there are apparently some sessions at Nostrasia 2024 on Sep. 23. 

 In Tokyo, small meetups are frequently held within the Nostr user community. However, rather than discussing the topic of Nostr, these are simply dinner parties where friendly users get together.