オプション☆モンスター, オプ☆モン or オプモン (OpMon) for short.

A game by Compile starring a girl named Momo-chan (モモちゃん) and the strange round weapon character Pom-kun (ポムくん). First released on DiscStation compilation discs for the "MSX":http://en.wikipedia.org/wiki/MSX system, but later rereleased for Windows.

* "Windows version on Amazon.jp":http://www.amazon.co.jp/dp/B00005OI99/
* "Gameplay video on NicoNico":http://www.nicovideo.jp/watch/sm5480647
option monster