Yuu is a member of Daath, given the title "the Gravekeeper of Daath". It was shown in episode 11 that he also possesses the Power of Kings like Shu. He works with Shuichiro into reviving Mana because when she matures into Eve she can form a new race with Shu who is her Adam, the person she chose to marry her.
He wears a long white collared coat with a black shirt and pants.
Yuu has a cold personality, and is implied to be looking down upon Shuichiro, who collaborates with him on his way to revive Eve. He expresses a cruel attitude toward Shu, but being a part of Daath, is implied to have some hopes in him for becoming Adam.
Like Shu (and later Gai) Yuu possesses the first Power of Kings, which allows him to draw out a person's Void, as shown in episode 11 when he tried to use Inori's Void to kill him.He can also make people unconcious by touching their forehead as in episode 12 when he puts Shuichiro to sleep after informing him of his failure.
His own Void manifests as a large bow, that can fire high speed arrows. When the arrow hits the intended target, it produces a series of metallic stripes that can completly bind it's target.