Risa Kagami is the late wife of Shiranuma (now known as Byaku). Worried that her husband would lose interest in her if she only had beauty to offer, which would eventually fade, she became obsessed with becoming eternally beautiful, and took her own life after becoming disfigured. The demon Kagami assumes Risa's surname and form as part of a contract with Heisuke Matsudo. Heisuke has feelings for Risa even tho she was married with Byaku and when she pass away Heisuke made an Ayakashi use her body to be his assistance. According to Byaku, Risa had the face of angel, but deep down she was a master manipulator, and he gave in to her every whim. She was the assistant to Heisuke Matsudo, and sought help from him about her worries of her husband losing interest in her because she wouldn't be eternally beautiful. Thus, Heisuke fell in love with her, obsessively. Her requests for the finest attire and jewelery didn't cease when she married Shiranuma. Shiranuma started experiments on her to keep her beautiful and make her immortal, and no matter what happened she always encouraged him. Until one night, one of his experiments failed and left her horribly disfigured. Shiranuma put a knife in her hand, left the room, and she stabbed herself in the heart. As she requested, he burned down their home and dug two graves, one for her and one for him. He buried her but left his empty. Sometime later, Heisuke dug up both graves. Seeing that Shiranuma's was empty, he assumed that he had taken Risa with him and ran off. But when he dug up Risa's, he saw her corpse and was stricken with grief. He took her body to his lab and did everything possibly to revive her, knowing full well that it was pointless to do to begin with. He gave up his efforts and summoned an ayakashi to whom he made a contract with, thus creating Kagami, who took her form and appearance. When Heisuke and Shiranuma (now Byaku) had their final battle, Heisuke asked him if he ever loved Risa. Byaku stated that he has never loved anyone in his life. (Source: kekkaishi.wikia)