Unless you already have some kind of Visa, they won't give you a tourist visa unless you have a scheduled return ticket.
Also currently they are cracking down on foreigners without a Visa, not only will the deport you, and refuse to let you return to Japan for up to 10 years, but it is quite possible to sit in jail for awhile before hand. And they charge you for sitting in Jail.
In addition, as a foreigner you do not have the same rights as here or that a Japansese national has. They can put you in Jail for weeks without allowing you to contact anyone.
Not trying to be a jerk, but I wouldn't go looking for trouble in a foreign country.
(and being a foreigner sleeping on a park bench will probably result in police coming around, you might get away with it if you were drunk, apologize, and can prove you legally are in the country with an address)