well, it all depends on
where you were going to live in japan. its a very big place you know, lol. like, living in tokyo will empty your pocketbook. lol.
200,000yen is about 900GBP.
and rent in itself is really big there. and then theres food (if you aren't used to asian cuisine, western food is available...but...its slightly more expensive....and living off cup noodles is easier said then done. lol)
and then social life will cut more into the remaining money. lol.
the amount of money you proposed would be more than sufficient though, looking at it from perspective. Jus don't over spend.
...