Practice elementary math!
These math problems can be tackled through a 'practice mode', a 'test mode', and a 'challenge mode.' The challenge mode is interesting because there are a collection of problems for each prefecture in Japan and if you succeed in each one you unlock various photgraphs to relax your mind with.
Although I can see why in this style of game you should practice first before testing yourself it stikes me as odd that you can only challenge certain prefectures after you have unlocked that style of questions or difficulty in the practice mode. In working through practice mode you also unlock a bunch of little interesting information cards with scraps of data about bento food, fish, vegetables, etc.
A language note: all these info cards are in Japanese, and the directions for the math questions are also Japanese. Some of the styles are obvious and you won't need the directions, but some are just bizarre and a decent grasp of Japanese would be necessary to know what to do the first time. However, none of the quizzes is so difficult that you can't figure it out by trial and error.
I believe you could import this if you wanted to and it might be worthwhile as I'm not familiar with anything like it available in the US right now. I would imagine the odds of this being released in the US are pretty slim too as this "brain power" fad is pretty big in Japan right now, but maybe not in the US.
In the end, I enjoy this game in short bursts because I like math and the challenge of being fast and flawless. But if you think all games need guns than steer well clear of this oddity.