The main character and his friends, Cheval and Lilia, are looking for a monster egg. They find a nest with one of them, and Rathalos hatches from it, who almost immediately becomes attached to the main character. They call the creature Ratha. However, upon returning to Hakum Village, she is attacked by a rampaging Nargacuga, possessed by a disease called the Black Plague. Ratha tries to protect the village, but appears to be killed. Cheval's mother, Vlau, also dies during the attack, driving him to despair.