Tokyo is a city of contrasts. Next to old streets and temples, you have skyscrapers with night clubs and coffee shops, with 'spirit of anime' at every step. Let's go for a virtual trip through the three most poplar districts. Each one has a distinct characteristics and leaves you with a different feeling.
Shinjuku is the most popular fun district in Tokyo. Noisy, crowded, full of night clubs, love hotels (hotel room rented per hour) with everything illuminated by neon lights. As curiosity, you can visit one of the 'host clubs', where pretty girls or handsome guys will court you with their attention and admiration. You can chose your 'host'. That's not a night club though. Meaning – there's no prostitution there. Hosts make your time only by talking to you over a drink. This kind of attraction is specific only to Japan.
Akihabara – Mekka of anime lovers. It's full of shops selling manga (Japanese comic books), CDs with cartoons, music and computer games, as well as plenty of anime gadgets (figurines, key chains, cosplay clothes). Those who are of age, get access to another floor of this kind of shop, that offers 'cartoons' and games for adults – so called 'hentai'. Let's just say that is an animated version of porn – another typically Japanese trait.
Akihabara is famous also for its 'maid cafes', where waitresses are dressed up as maids. It's a common Japanese fetish. Unfortunately in this kind of cafe, except for the order (which isn't the cheapest), you also have to pay the entrance fee (500 yen ~4,5$). You also have to wait in the line in front of the door, even if the shop is completely empty. So before you can get 'soothed' by the helpful maids, first the bouncer or manager will give you appropriate vermin treatment. I must admit that I was largely disappointed in this attraction.
Another curiosity... In Japan places where you can pet various animals gained popularity. In Akihabara I found a 'hedgehog cafe'. They call it 'cafe' but due to sanitary reasons, you won't get any snacks or drinks. Entrance ticket allows you to get one bottle of soda from the vending machine inside. The attraction here is that you can pet a hedgehog. I don't recommend coming in the morning. Hedgehogs are nocturnal and they sleep during the day. If you want to 'play with the hedgehog', it's better to come I the evening.
Asakusa – part of 'old Tokyo'. It's main attraction is Sensoji temple and a close by shopping district. If you're looking for souvenirs from Japan go there (unless you're planning visit to Kyoto as well. Then I recommend buying your souvenirs there).