[Steam page] Developed by Japanese studio, Toylogic, Happy Wars is now available for the PC platform via Steam. Currently in its Early Access phase, Happy Wars is a Free-to-Play team-based online game which features 15 vs 15 combat. I was told the game is really popular on Xbox 360.
Official description: Happy Wars is an action-packed massive online multiplayer game where you can play together with as many as 30 players in one online session. Team up with players all over the world and go crazy in wacky melees in a fantastic realm of heated sieges and big magical battles!