Shiina Yuya is a bounty hunter interested in the largest bounty she can find, that of 1,000,000 ryo that is on the head of Demon Eyes Kyo. She decides to follow Kyoshiro, bonding with him until he is "put to sleep" by the reappearance of Kyo. When Kyo wakes up completely, she follows him. In spite of his attitude, she comes to trust and believe in Kyo. In the forest of Aokigahara, she learns that Kyoshiro killed her older brother and decides to wait until he returns to the surface in order to get an explanation from him. Yuya is thus interested in Kyo and Kyoshiro. Somewhere deep in her heart, she knows the valuable secret of the Mibu Clan, a secret that her brother Nozomu shared with her when she was very young. The Aka no Ou also comes to believe that she is a seer, but this is neither confirmed nor disproven. In Chapter 229 of the manga, while telling her brother that she would not forgive him if he killed Kyo, she admitted out loud in front of everybody that she was in love with Kyo.
Despite being very temperamental and even violent if irritated, Yuya has a gentle and kind personality. Besides Kyo, Benitora and Akira have a crush on her. Many other characters come to enjoy her company and regard her as an important friend whom they will protect. At the very end of the manga, Yuya is searching for Kyo and in the bonus chapter Kyo and Yuya live together.