Legion introduces the story of David Haller (Stevens), based on the Marvel comics character Legion, the son of X-Men founder Charles Xavier. Since he was a teenager, David has struggled with mental illness. A haunted man, David is getting tired of finding his way back to sanity and is about to give up when he meets the girl of his dreams, a fellow patient, and is confronted with the possibility that the voices he hears and the visions he sees might be real.
Midthunder will play Kerry, a woman of action with a childlike sense of wonder. A true savant, Kerry has lived a sheltered, but never dull life.
The actress, repped by Stone Manners Salners Agency and Corner Booth Entertainment, will next be seen in the feature Comancheria starring Chris Pine and Ben Foster.