Kasumi Gyoubu was one of ten ninja chosen to represent the Kouga Manjidani clan in their duel against the chosen ten of the rival Iga Tsubagakure clan.
Tall, bald and powerfully muscled, Gyoubu is strong enough to break an enemy in half with nothing more than his bare hands. Despite his massive size though, Gyoubu's specialty is stealth. By merging with the surface of an object, Gyoubu is able to move and attack in complete secrecy as well as manipulate any object in physical contact with the surface. There are limits to his abilities however:
The surface area of an object apparently must be at least equal to his own in order to merge or move on and it must have physical contact with a surface of similar dimensions in order for him traverse from one to the other; Only his body can merge so he must strip naked as well as drop any weapon he carries in order to use his technique. Merging offers him no defensive benefits, as any attacks to the surface of the object transfer to him as well.
Like most of the Kouga, Gyoubu bears an overwhelming hatred for the Iga. Although in the anime Gyoubu's rage is more of a personal vendetta. Years ago, Gyoubu's father Renbu was murdered by an Iga squad and Gyoubu vowed to one day take revenge, since his father's last words were to never pity any ninja. Unfortunately, the Hattori truce was imposed on both clans shortly afterward and Gyoubu shaved his head as a statement of his unsatisfied fury. A portion of his rage seems to be reserved for himself as he confided to Muroga Hyouma in episode 11 that if he hadn't been so weak as a child he would've been able to better protect his father, which explains why Gyoubu trained his body to become a mountain of raw physical power. In the anime, Gyoubu shares an uncle/niece bond with the tomboyish Okoi whom he frequently takes with him to go hunt wild boar in the forests surrounding Manjidani.