I lived in Japan for many years until recently and had my own start-up with two other co-founders. The company is still going (and quite successfully I might proudly add).

There are many start-up companies over there across all industries. There isn't really a clique/community like there seems to be in San Fran, Sydney (my home town) etc. Founders just start up out of opportunity and need.

There are also open desk places for start-ups. A lot of that seems to be mainly occupied by creative design companies. In saying that I think you'll find most start-ups are not tech based.

If you'd like to know more shoot through some specific questions and I'll see if I can help you or even introduce you to the appropriate people.

I seem to not have answered your question with the above.

If you are eligible for a work visa get it before heading over. A common way to get a work visa if your two countries don't have a working holiday visa agreement is to apply for an English teaching role in your home country and then when you enter the country use that work visa to springboard into another job (note: this normally means you have to teach English for several months which can be hell if you don't like that sort of thing).

Already having a job ready for you when you arrive is the best way but highly unlikely a start-up is going to go through the process of sponsorship for your visa.

If you have 100K to spare you can go over there establish your own company and then sponsor yourself. You can then pay yourself an annual salary of 100K and get that money back. Little bit dodgy but within the law. At least the way I did it was!

Expect to get 200,000-300,000yen/month for a real beginning of the journey start-up company. If it already has a steady and growing revenue stream then you can probably negotiate higher.

If you are open to one-step-above-a-backpacker's-hostel living arrangements I suggest you get a room with SakuraHouse (if you plan to stay in Tokyo -- also advised if you want to work in a start-up). As it is cheap and easy to cancel the contract. Once you get a feel for the place then look to set up more permanent digs. Also look through the classifieds on www.metropolis.co.jp which is a local rag for foreigners living in Tokyo (you probably want to do the whole complete Japanese immersion thing but finding a Japanese sharehouse will be more difficult than a foreign sharehouse).

Winter is feezing, Summer is humid. Be prepared!

It is an amazing place.