I see. In that case... Economics departments are not so prestigeous in Japan... The highest ranked is 107th in the world, and that is at Osaka University.
http://www.uoguelph.ca/~tstengos/eearank93.pdf
Don't take this as fact. It's just one of many rankings, but in my experience, I've never seen Japanese Universities ranked highly when it comes to Economics.
On the other hand, if you're looking for prestige, then the subject you do, doesn't really matter. It's usually the name of the university that counts, not the course. Please not, "usually", and this isn't true for all cases. But that's up to you to find out if it applies to you by ressearching your career options.