Grimm is a Yellow Comet CO and a protagonist in Advance Wars: Dual Strike. He is a student of Sensei and a member of the Allied Nations forces stationed in Omega Land. He has a very impulsive and daredevil personality, and does not care much for things such as planning, instead preferring to rush into battle.
Grimm was a member of an Allied Nations force sent to Omega Land to defend it from Black Hole along with his mentor Sensei. They succeeded in stopping the Black Hole forces from draining all of Omega Land to give their leader Von Bolt eternal life, with defecting Black Hole CO Hawke stealing Von Bolt's chair and using it to restore Omega Land to its green state.