Yup I have my fair share of encounters in the kaikans of Ueno and Asakusa. I skip the one in Shinjuku as its more of a hangout for the lean and hunky type...and hardly any matured or uncles.
The most eye-opening thing I have come across (so far) should be the live fisting session that I saw in the kaikan in Ueno early this year: 2 men were taking turns to fist a 30-something...and after that it turned out to be man A fisting man B who is fisting man C kinda thing. Quite corn starch for some of the audience there but I must say I was just...surprised and awed and....yuck!
One of them even gestered to me to join them...maybe he wanted to fist me as well (?!) but no thanks, I'd love to just be a nice quiet audience for this one.