He was the guitar player and song writer of the band Crow. After meeting with Tendou Kodzunu, he gains the power of vibration and frequency. At one point he even turned into a crow-like demon. He was the one responsible for the Crow Incident.
He seemed to be very protective of things between him and his friend, and former band member, Raito Umon. After gaining demon powers, he becomes very destructive and even caused the death of Sayo Hirasaka, though she wasn't a specific target.
Around the time Ryouichi and Raito were having issues, he was visited by Tendou Kodzunu and give demon powers. As a result, his mind had become twisted and he became a threat to society due to how dangerous and destructive his powers were. After Tatsuma Hiyuu and his friends had taken him down, he was killed by Tendou.
"Karasu" means "crow" in Japanese.