Yosuke Otoha is the main character in Karas.
Otoha is Shinjuku's last hope since every Karas before him has fallen before Eko. He is a powerful Karas and was even feared in the human world. For some time in Revelations he lost his powers because of the death of his Yurine. Eventually he regains his powers upon his Yurine being revived and puts an end to Eko.
After the first intro scene of Karas The Prophecy, a barely conscious Otoha is seen being rushed into a hospital. It is eventually revealed that one week prior to that he and his friend Reiji were robbing someone and Otoha, protecting Reiji, had been shot. The bullets were enough to send him flying down several flights of stairs and eventually falling into a stack of cardboard boxes. It is revealed a little later someone rushed him into the hospital claiming he fell from the sky. Prior to those events, Otoha did work for the Yakuza and was often feared as a monster who has no emotions and doesn't feel pain.
When he awakes from his coma he goes and saves Reiji who is badly beaten in the back of a bar. After leaving the bar for just a few minutes cops are called to the scene and his brother-father shoots Reiji in the head, killing him. Otoha is shot in the knee from his brother-father, but Otoha is still able to run up to him and slice his gun. His brother-father calls him a freak and wishes that he had killed Otoha the day he was born. Otoha then proceeds to kill his brother-father and the yakuza open fire. Right before Otoha is killed, he is saved by Homura (A Karas from another city). She claims that she only saved him because her Yurine told her to (Although it is revealed in Prophecy that Homura likes Otoha to some extent, even though in Revelation, Otoha's Yurine and Otoha, himself almost kiss each other).
Later on Otoha rushes to save a little girl from the tentacles Eko had conjured up and also tries to kill Ushi-oni, nearly dying while doing so. These details are important because his will to continue to help the city is what gives him his Karas powers back and revives his Yurine. When his powers are revived, he kills Ushi-oni and proceeds to kill Eko. Before Eko dies he tells Otoha that he will see things like he does after 400 years of being a Karas.
At the very end of the movie Otoha is seen in Karas form standing on a statue with Yurine perching on his arm.