Raging obesity is not such a huge issue in Japan compared to countries like the USA or Russia (though I hear McDonald's is gaining foothold). Ironically enough, they nevertheless have a strange obsession with Sumo Wrestling over there – two incredibly fat guys basically turning into a big mass of jelly.
Aa Harimanada apparently began its life as a comic book which later managed to take the leap into an animated cartoon and from there into this console game. What the plot is exactly, I can't tell you as all these publications (including the game) are available in Japanese only (a language I don't speak at all). It probably doesn't help that I'm also no expert at the rules of Sumo Wrestling (still an understatement). What I do know about this sport is that it is basically about pushing the opponent out of a confined circle.