Sothis

Sothis is a character and the deuteragonist of Fire Emblem: Three Houses. She is a mysterious and amnesiac girl that only Byleth can see. Sothis is also the Goddess of Fódian and is the mother of Serios.

Her goal is to help Byleth out by saving Fódian and possesses a major Crest of Flames. Near the end of Fire Emblem: Three Houses, she fuses with Byleth to defeat their enemies.

She is voiced by Tomoyo Kurosawa in the Japanese version, and by Cassandra Lee Morris in the English version, the former of the latter who also voices Morgana in Persona 5, Rachel in Glitter Force Doki Doki, Suguha Kiriyaga/Leafa in Sword Art Online, and Kyubey in Puella Magi Madoka Magica.

Appearance
Sothis is a young girl that bears resemblance to a 16-year old girl with beautiful, long, green hair and eyes, wears red earrings, and yields a sword, and wears a purple dress with gold details.