A lonely psychic girl who has a connection to Watanuki. She writes her surname with the characters for May 7th, similar to how Watanuki writes his name with the characters for April 1st. Her mother has distanced herself from Kohane, treating her more as a commodity then her child. Kohane's mother even refuses to touch her, for fear that she will lose her powers. Watanuki befriends Kohane and takes it upon himself to try to protect her.
She mentioned to Watanuki that she hasn't been called by her first name as far as she can remember, marking Watanuki calling her "Kohane-chan" as a first. Her first name in kanji is translated as "small feathers" and her last name literally means May 7.
She and Watanuki seem to share a bond, likely because, due to their spiritual abilities, they have both been exposed to the occult at a young age. However, her mother is vehemently opposing to their friendship, dragging Kohane away any chance she sees Kohane with anyone especially Watanuki and company. It is revealed in the end of chapter 156 of the manga that her power to exorcise spirits came from one of Princess Sakura's feathers(See Tsubasa Reservoir Chronicles for details)
During an incident of a live TV show where she and other mediums were asked if they sensed different spirits of a haunted place, Kohane's deductions of another spirit present was different from all the other mediums who had sensed the same thing. This caused her to be labeled as a hoax, even as far having her house vandalized. In chapter 137, Watanuki sees her covered in wounds and bandages after "falling" down the stairs on her way home (she suspects she was pushed, though seems indifferent).
an extended description!