I am going to answer this question myself because I have looked into this subject just recently and I know what Tokyo twitter life is like :)
It was actually a small project to accompany http://akihabara.tokyo and the goal was to see how active English speaking users in Tokyo are. Twitter API allows you to collect tweets by specifying a number of parameters. I used only two: language (English) and location. For location I specified coordinates that very approximately correspond to the area of Tokyo and its nearest suburbs. This results in over 1000 tweets every day. There are probably more because not everyone publishes their geolocation. But 1000 tweets every day is more than enough to get an idea of what's Tokyo is tweeting about. To be honest Since the beginning of the experiment I have not been able to look through all the thousand tweets for the day.
I have not done any real analysis but I can share my impressions:
I will keep looking at Tokyo tweets and will probably post more observations in the future. Meanwhile follow our account @akbtokyo