Kurogane is a ninja who is sent away from his world by Princess Tomoyo in order to have him discover true strength. He is the most powerful warrior in his world, but he shows no mercy to anyone, even at Tomoyo's request, so she places a "curse" on him that will decrease his strength if he kills anyone. He gives up his sword,Ginryū (Silver Dragon), as the price to use Mokona to cross dimensions and return to his home world. He quickly bonds with Syaoran, who he trains in swordsmanship and helps overcome his blind right eye. He is constantly teased by Fai, who calls him a variety of nicknames, though he also is able to tell Fai's true nature, and Mokona, whose cute nature Kurogane cannot stand, preferring to refer to Mokona as a "white dumpling." Though he initially has no interest in helping restore Sakura's memory, he eventually finds himself risking his life for the group.
[Edit]Kurogane's parents were murdered when he was a little boy, but before that, he trained under his father in swordsmanship, wishes to become stronger so he can protect those he loves, and he cares for his mother, who has tuberculosis. Eventually, Fei Wong Reed floods the area with demons, which leads to the death of his father, and Reed personally kills Kurogane's mother through a dimensional portal. Kurogane goes into a rage, killing all of the demons while grasping his mother's body, and he is only calmed by Tomoyo. He eventually becomes a personal retainer for Tomoyo, but his ideals change from protecting those he loves to just gaining strength and finding his mother's killer. He eventually learns that the whole attack is part of Reed's plan to make him a pawn, but interference from Yuko causes Tomoyo to reach him first.
In Tsubasa Reservoir Chronicle OAV, Kurogane cuts off his left arm to save Fai, but when they return to Nihon Country, he is granted an artificial arm from Piffle World. There, Tomoyo told Kurogane she did not burry his fathers sword do to the request of his mother. He soon learns that the curse Tomoyo put on him was actually a protective charm, and notion of losing strength was actually the lose of his arm, though it also helps him realize that "true strength" is protecting those close to him.