What Happened to Corrin is the thirteenth chapter of Fire Emblem Warriors.
In search for Ryoma, Xander, and Corrin, the party finds Ryoma and Xander in the forest at night. However both princes start attacking the party, evetually revealing that someone brainwashed them. During the fight, Corrin reveals herself but is brainwashed as well. It is revealed that one of Gristonne’s recruited villains, the former Nohr tactician turned traitor Iago, was responsible for brainwashing Corrin, Ryoma, and Xander. This also explains Corrin’s sudden disappearance, which caused both Hoshido and Nohr to blame each other earlier.