[Nyororin]

Even if you don`t get caught living there. Even if you manage to hang around quietly and no one notices you...

Someday you will want to leave the country for some reason or another - and you will need your passport. And they will check your passport.
You see, those stamps and stickers in the passport aren`t just for decoration. They contain info about your stay... In other words, when you came into the country and how long you are allowed to stay. So you WILL be caught if you ever try to leave the country, as it`s necessary to present your passport to do so.

I imagine it would be possible to live the rest of your life quietly and secretly inside Japan, never owning property, never getting married, never getting a credit card, never buying a car, never having a decent job, never renting anything, etc etc... But really... What is the point?