A mage found in Alm's route. The rest is a quote from the Fire Emblem Wiki.

"Despite being naturally gifted with magic, Delthea is not interested in training her abilities, using it in Alm's group because she likes helping him, only to seal it after the war. She is bright and cheerful, though a bit of a selfish young girl. Constantly making fun of Luthier, her supports make it clear that she does love him and would like to be friends deep down, quick to defend him when Clair does the same."

Delthea's english voice is Christine Marie Cabanos. https://youtu.be/4tr3F08iwv0?t=1591