Karin is a girl who greatly resembles Sheela, the princess that Shura was in love with centries ago. When she was little, she moved away from the town above the Lid of the Kettle of Hell right after the tragic death of her parents. Then when Arima Kouyou became her foster father, she moved back to her hometown. Karin's best friend is Ninomiya Asako, whom Karin knew before her parents' death, and whom Karin immediately reunited with upon moving back.
She is an extremely gentle and kind-hearted person. When she first found out about her resemblance to Sheela, Karin wondered if she might have been Sheela's reincarnation. But after learning the horrid way Sheela was consumed by Deirdre, down to the very soul, such that Sheela could not have reincarnated, Karin became oversensative to Shura's pain, and feared that her very presence was a cruel reminder to Shura of Sheela's death.
She is the mother of Katsuragi Kira.