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.
Appearance
He wears a long white collared coat with a black shirt and pants.
Personality
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.
Abilities
Void Genome
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. Like Gai he apparently draw out Voids without physical or eye contact, through unknown means.
Yuu pulling out Inori's Void
In episode 12 he showed his powers extensively, using multiple Voids of several Daath followers gathered there to fight Shu. He showed skill in dual-wielding several Voids such as dual-whips, swords and chakrams and discarded them at a whim.
Like Shu and Gai he can combine Voids to produce more powerful ones, as shown when he combined dozens of Voids to produce a large double barrel cannon to kill Shu.
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 the target.
Other abilities
Beyond his use of the Void Genome, Yuu also showed several abilities no other character has shown so far. he has displayed the ability of levitation in several of his appearences and the ability to render a person unconscious with a touch to the forehead as shown in episode 12 when he puts Shuichiro to sleep after informing him of his failure.
In episode 12 he displayed telekinetic abilites by stopping and redirecting a flurry of bullets by Argo as well as the ability create energy shields and the ability to de-materialize and materialize at will from one place to another.