Losaria is the protagonist of Shadowverse's tutorial, as well as the best friend of Arisa. She was training to become a forest guardian with her, before being taken away by the Shades.
It is found out at the end of Arisa's chapter of 01: The Morning Star that Losaria was used as the host of Nexus, the first keeper introduced in the game.
Losaria is a leader representing the Forestcraft class. Currently, she cannot be played outside of the tutorial.