During the Peace Walker Incident, the Militaires Sans Frontières encountered Rathalos on Isla del Monstruo after being invited to the island by the Felyne Trenya. It attacked by spitting fireballs, charging, tail-swings, and swoops. Chico claimed that Rathalos was in an old Pirate Lore book of his and implied that it may have been responsible for attacks on ships in the middle of the ocean.