Leo (レオ,reo?) is known as the White Knight of Althena in Lunar and is one of the Four Heroes. He is also the brother of Mauri and best friend to Ronfar. He is a loyal member of an organization called Althena's Guard, a group charged with bringing the message of the Goddess Althena to Lunar and stopping all wrong-doing in the name of the Goddess. Leo vigorously pursues a being known only as "The Destroyer", said to bring catastrophe to Lunar. Leo is considerably powerful and is said to wield the power of the White Dragon. He pilots the Dragonship Destiny with great pride and skill.
When Leo begins to learn the true face of the Chosen of Althena, he begins to question himself and cannot bring himself to face Hiro and the others, admitting his mistakes in doing so. He takes on the identity Mystere (仮面の白騎士,kamen no shirokishi?, "Masked White Knight") to help the party as a way to atone for his mistakes without actually having to take responsibility for his actions.