The nightlife is on its way up
Tokyo has amazing jazz clubs: the Blue Note, the Cotton Club, Billboard, the Shinjuku Pit Inn, and some smaller clubs you'll have to ask around for.
There are fantastic nightclubs like WOMB where you can get your groove on. And this year the ban on dancing after midnight at nightclubs (Holy Footloose -- yes, such a thing existed) was finally lifted so the nightlife is coming back from the dead.
For grown-up adventures, you can try theme bars like the Robot Restaurant, which combines a stage show with animatronics, traditional Japanese drumming (taiko) by beautiful women, Disney-esque storylines, and a nonsensical series of performances that will leave your senses pleasantly obliterated. Then you can stumble to REN, the sister bar of the cafe, and enjoy karaoke or live performances in a hallucinogenic setting. All of this is in the heart of Kabukicho -- which is to Tokyo what the old Times Square used to be to NYC. The themes may offend some. The Christon Café is a church with unholy cocktails. Alcatraz ER combines the prison-themed restaurant with an insane-asylum meme and serves booze in IV bags; if you're lucky, a buxom nurse in a slightly bloody uniform will bottle-feed you alcoholic beverages.