I've long believed that it's around the third year when people decide if they're going to commit to living long term in Japan. The reasoning is that the first year is new and different in all the good ways ("it's so safe, the staff in the shops are so attentive, the festivals are so fun!"), the second is when things are new and different in the bad ways ("they're so inflexible, the summer is horrendous, and the people at my company work 24 hours a day"), and the third year is where you weigh up the pros and cons and decide whether to stick with it or not.
This is only an idea, of course. Some people may decide very quickly, and others may still be uncertain after many years and others won't have a "single moment" but an accretion of many moments. But whenever that moment came to you, what was the main reason for staying? (I'd say "reason for leaving" too, but as this group seems to be strict about only people living in Japan posting).
Personally I didn't have a single eureka moment, and my motivation was more about "not having to go back to the UK" then "wanting to stay in Japan".
by Tasty_Comfortable_77