Throughout the story, Dan only wants to see his sister Doris out of danger. Dan looks up to D even though people say he's dangerous. Both he and Doris believe D is a good person despite what others say. Dan, however, thinks he should take care of Doris himself. He does not want to see her harmed in any way and does whatever he can to help her. Although sometimes his actions get him into trouble. (Source: Absolute Anime)
