Sothis

Sothis is a character from Fire Emblem: Three Houses. She is a mysterious girl that only Byleth can communicate with. She possesses a major Crest of Flames.

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Sothis first appears before Byleth in a dream, asking for their name and birthdate. By sheer coincidence, the two share the same birthday. However, she quickly falls back asleep and the dream ends.

Shortly after this dream, Byleth alongside their father Jeralt are asked by some young students to help them repel some bandits. While most are dispatched, the leader, Kostas manages to ambush Edelgard and Byleth leaps between the two. Just as Kostas's axe is about to strike Byleth, time suddenly stops as Sothis uses her power to freeze time. She berates Byleth for their recklessness but is suddenly shocked by the fact that she is now able to remember her name. Pondering Byleth's fate, the two realize that Sothis not only can pause time, but also rewind it, granting Byleth a second chance to redo their rescue, this time disabling Kostas. Sothis continues with Byleth, speaking directly to them telepathically, unseen by the rest of the world.

Using her power to rewind time, Sothis saved Byleth's life from bandits. She does not physically appear, appearing only inside Byleth's mind, so nobody except them knows of her existence. She grants Byleth the ability to use her time manipulation power called Divine Pulse. Sothis seems to have lost all recollection of her past, but does remember calling the Red Canyon home.