Breath of Fire (ブレス オブ ファイア Buresu Obu Faia) is a RPG series developed by Capcom, the first game being released for the Super Nintendo Entertainment System in 1993. The games have an ambiguous continuity, but the names of two protagonists are always the same: Ryu and Nina. Each Ryu is a man with blue hair able to transform into a dragon, while each Nina is a blonde woman with wings.
The Breath of Fire series only had minor appearances alongside the Mega Man series in video games, such as cards in the SNK vs. Capcom: Card Fighters series and Ultimate Marvel vs. Capcom 3, and costumes of Mega Man, Roll, Mega Man Volnutt and Tron Bonne in Breath of Fire 6. Characters from Breath of Fire III appeared in the Archie Comics crossover Worlds Unite.
When Sigma sends several Mavericks to different worlds, Toxic Seahorse and Spiral Pegasus attempt to set an Unity Engine in the Steel Grave, but are stopped by Ryu, Nina, Garr, Momo, Honey, Rei and Peco. After the battle, Momo looks to the Unity Engine and rightly guesses what its purpose is, and Hard Man and Big the Cat appear to explain the situation. They later participate in the battle against Sigma alongside heroes from other worlds.