Dario is a boss fought in Chrono Cross. After the rescuing Riddel from Viper Manor in Another World, the Mastermune quest can be completed by defeating Dario. First, the party should visit Viper Manor and enter the area previously blocked by the Guillot and obtain the note from the trap chest. Next, Karsh should visit the Isle of the Damned, where he sheds some light on Dario's disappearance. The party should then bring Riddel to the smoking island near Mount Pyre where she will find Dario and awaken his memories. Unfortunately, Dario is possessed by the Masamune and the party must defeat him to cleanse the Masamune and release Dario from its curse. When victorious, Serge will obtain the Mastermune.