If there is a single member of the Ten No Ryuu with whom Seiichirou is the closest, it is Kasumi Karen. They are very close friends, though his marriage prevents them from being anything more. Even if he can not give Karen his heart, he can give her the one thing she really wants—he has promised to cry for her when she dies.

While his career is mundane and average, she works in a bath house, wearing negligee while washing her male clients. Despite the nature of her work, she regards it dispassionately as a service job. The two originally met when he came to her bathhouse while doing research for a writer and interviewed her. They had an immediate rapport even before knowing that they would be working together to save the world. During the course of their interview, he refers to her “precious life”--a remark which has a major impact on her. She goes home and writes a letter saying she hopes to meet him again.

Like Seiichirou, Karen embraces her destiny to protect the Earth. Despite the pain and unkindness Karen has encountered, she still believes that the world is worth protecting, and is willing to give her life for her cause. She finds comfort in knowing that her powers, which seem so useless to her in the modern world, have some value in the long run. Unlike Seiichirou, who comes from a clan of Windmasters, Karen has spent most of her life as an outcast because of her fire power.

There is no doubt that Karen had a damaging childhood. Her religiously fanatic mother beat her for her fire powers, calling her a monster and saying that no one would cry for her when she died. When her mother died, Karen believed that she had lost the only person who would ever care about her. Not only that, but she had to contend with cults which pursued her for her powers. Still, she is a relatively happy person who escaped into the world of the Pleasure District to avoid inquiries into her past.

Destiny and the fate of the Earth bring them together again. The two become a fighting team, working together against the increasingly powerful Chi no Ryuu. At one point, Karen decides that she will fight alone because her life is not as valuable as those of her fellow Ten no Ryuu. Knowing that Seiichirou would never let her go alone willingly, she puts something in his tea to put him to sleep while she goes off to battle. To fight off the effects of the drug, he stabs himself with a small knife and comes to her aid. Despite his calm nature, he tells her never to go off alone again or he will get very angry. His concern for her really touches Karen. From that point on they fight as a team.

Although she is in love with him, she knows that he loves his family and does not act on her feelings. Although she confesses that she is a little jealous, she is far too moral to do anything to jeopardize his situation. She loves him from afar, and is content to be his friend. He, in turn, loves her as a dear friend and would do anything to protect her. His friendship is enough for Karen, who has been alone for most of her life.