Fuuma Monou

The primary antagonist and Kamui's dear friend. Fuuma is initially kind and gentle. He helps his father dutifully and dotes upon his younger sister Kotori, and excels at high-school sports. After Nataku attacks Kyogo and steals the first Shinken, Fuuma's dying father tells him that he is Kamui's twin star. Accordingly, when Kamui chooses the Dragons of Heaven, Fuuma is forced to become a Dragon of Earth, immediately attacking Kamui. He proceeds to grant wishes to the characters with whom he interacts, in ways that often lead to their death or that of a loved one. Tsubasa: Reservoir Chronicle

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He is Seishirō's younger brother, a friend of Yuko Ichihara and de facto leader of the people of the Tower. In actuality, he's a treasure hunter who can travel across dimensions and often searches artifacts at Yuko's request. He is on friendly terms with the main characters in the series.