Yuu(ユウYū)appears in Rei Gaiden as a young girl who meets Rei on his journey. She originally diguises herself as a boy and pretends to be a master of Nanto Seiken, donning a girl "disguise" on top of that to lure bandits in and steal their supplies (something Rei later adopts at a much more subliminal level at his introduction in Hokuto no Ken). After Rei saves her from bandits with his Nanto Suichō Ken, she agrees to take him to Asgarðr in his search for Airi. When she was young, Yuu's mother died in the desert during their journey to Asgarzul and she was adopted by Eva. She often distanced herself from her sister's ways, however, only growing to adopt them after Eva's death.