Noyama

Koharu Utsumi's Brother is a young Ghoul adopted and raised by Yuujirou Utsumi, a wealthy human. Along with his sister, he was responsible for providing the family with young girls to eat. After the death of his sister and his father's hospitalization, he murdered a family friend and then vanished.

Appearance
He appears to be an average young man, with short dark hair. His mask is noted to be decorated with beautiful, elaborate embroidery.

Personality
He is described as a rebellious and troublesome young man, always just barely controlled by his adoptive father. While Koharu felt remorse for her part in her family's crimes, he readily took part in them and even takes steps to cover his tracks afterwards. He is shown to have a dislike for his sister, treating her with disdain and acting violently towards her to the extent that Amon mistook him for a criminal blackmailing her.

Past
Presumably, at some point in his childhood, Investigators killed his parents and left him orphaned. Along with Koharu, he was adopted by the human serial killer, Yuujirou Utsumi, and raised as his own son. While Koharu was responsible for capturing the girls, he was responsible for the "dismantling" of their victims -- suggesting he was the one to actually kill and prepare them for food.

Heat Haze
Koutarou Amon comes across him arguing with Koharu, who gives him an envelope filled with money. When the Investigator tries to intervene, he quickly leaves the scene. Koharu defends him from Amon's suspicions, refusing to explain but promising nothing criminal was going on.

Embroidery
He spends some time stalking Tsumugi Yamagata, an old friend of his father that provided him with his mask. After the old woman visits his father in the hospital, the young man ambushes Tsumugi and Asa. He seriously wounds them both, but flees when confronted by Uta. Tsumugi dies of her injuries soon after, explaining that she knew he was intending to kill her out of fear that she would reveal what she knew. After killing Tsumugi, his whereabouts are unknown.

Power and Abilities
Unlike his sister, he is noted to be a Ghoul of moderate strength and extreme aggression. He is strong enough to seriously injure Asa, but flees when confronted by a Ghoul as powerful as Uta.
 * Ukaku Kagune: His kagune takes the form of a pair of dragonfly-like wings, which he can fire projectiles from.

Yuujirou Utsumi
He is described as having been extremely rebellious and barely controlled, suggesting a poor relationship between them. Once free of his family, he takes off on his own with little care for what happened to his father.

Koharu Utsumi
Their single interaction shows that they did not get along, with him yelling at her and treating her poorly. His actions caused Amon to suspect him of being a criminal out to harm Koharu, as a result of his violent treatment of her.

Tsumugi Yamagata
Though she had been a friend of the family for many decades, and provided him with his mask, he considered her a danger. As such, once free from his family, he set out to eliminate her so that no one alive would know about him.

Trivia

 * While never explicitly stated to be her blood relative, it is likely that he is Koharu's biological sibling due to their near-identical kagune.