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She is a pretty young girl around Chizuru's age, with long brown hair. She is a pureblood Oni, but because of Kimigiku, her bodyguard, Kazama Chikage doesn't chase after her, going after Chizuru instead. Sen is first introduced when she protects a child and is threatened by a group of men. Chizuru jumps in, forgetting that she cannot fight very well, and Saito Hajime steps in, knocking the men out with the blunt side of his blade. She later reveals Chizuru's real heritage, even offering twice for Chizuru to come with her and Kimigiku to be better protected.

Source from Wikipeida