So I made up my mind and will apply for a working holiday visa. There is an information office in the Nakano ward, not far away from the train station. The building looks really exceptional with its big clock on the one and the “ski slope” on the other side.
Still, I first went through the Nakano Broadway, a shopping mall. The first floor sometimes looked quite trashy, especially one shoe store. Funnily, the Broadway is part of the Yokoso campaign to visit Japan. Later, I read that there are some cool anime stores on the second floor but I didn’t came to look for anime, so I stayed on the first floor. At the end of the mall is a 100 Yen store with three floors.
The working holiday information office was not hard to find, once I was in the building. It’s up on the seventh floor. Well, the office lady couldn’t tell me anything which I couldn’t look up on the internet but they may help you e.g. to find a job or a place to live. Probably useful for people who don’t want to spend hours on the net to find everything they need to survive in Tokyo.