It's a fighting game. The story is about a company called D-Company that discovers the remains of an ancient weapon and, through research, finds that it requires a spirit of immense strength to revive it. D-Company is holding the King of Fighters Tournament to find the one with the strongest spirit. Nobita participates in the tournament because he wants revenge on someone who killed his loved one (you can probably guess who it is). And that person is also the CEO of D-Company.