Mousen (毛旋) is a guard of the king of En. He initially serves as a non-commissioned officer under Seishou. Mousen regards the king of En with a sort of "he can't be helped" kind of attitude in the sense of "let's just let him do what he wants."
While he worries about how Shoryu secretly leaves Genei Palace without any word about where he is going, Mousen doesn't bother trying to stop him because he knows that he will be unable to stop Shoryu. During the rebellion in Gen Province, Shoryu temporarily appoints him as the Daishiba of the Ministry of Summer in order to gain control of the Royal Army.