Iku Yuuki

15 year old, and Yori's twin sister. In contrast to Yori, she is dense and clumsy, but has a determined spirit. She loves Yori deeply and was shocked when he confessed his love to her. At first, she is worried and torn between returning her brother's feelings vs losing him by rejecting him. She eventually decides that she indeed loves Yori as a man. Like Yori, she feels content with their taboo relationship, but knows how wrong it is. Halfway through, she learns that Yori is actually her half-twin brother. Even after Yori's unexpected departure and Yano's confession, Iku says that Yori is the only one she loves and vows to find him. In the climax, when they reunite, it is presumed that they continue their relationship.

(Source: Wikipedia)