Decabar is a bar/club in Kabukicho Tokyo that hosts a variety of events from DJs to foam parties to a weekly Dominatrix night. It's also somewhere you can just go when there's no event and maybe bump into kinky people. Recently it has been the venue for a regular monthly casual munch for kinky people on a Saturday afternoon.
How wild you can get depends on the type of event that night. It's not a happening bar so don't expect people to be naked or having sex.
You'll see their very colourful sign at the bottom of a group of signs on the building. It's on your left if you're coming from Shinjuku station, opposite an alleyway full of tiny bars. Go down the stairs, it's straight ahead.