I went to this event a year or two ago, I happened to be passing through japan. It's a very friendly event, real mix of different tech / startup presentations. Would highly recommend it if you're in the area :)
I've not been to the Tokyo meetups, but I certainly enjoyed the HN Kansai meetup. I met some interesting people hacking on (somewhat niche) fun things - game dev, web design, cryptocurrency, etc. Definitely recommend it!
Yes, confirmed - however we announce the meetups on these pages:
Meetup.com https://www.meetup.com/Hacker-News-Tokyo-Japan/
Doorkeeper https://hntokyo.doorkeeper.jp/