Hyō

is a member of Konohagakure's ANBU faction: Root.

Background
Like most Root members, he's still loyal to Root's founder Danzō Shimura and is apparently trustworthy enough to be given the task of delivering top-secret information for him.

Abilities
Although Hyō hasn't displayed any techniques, he is able to sneak up on Sai without being noticed until he strikes, implying that his stealth is on a high level. Like all members of Root, Hyō carries a tipless tantō, which he seems to be skilled with.

Sasuke and Sai Arc
He is introduced when acting as a go-between for Danzō and Sai, reminding the latter about the will and purpose of Root while doing so. He's also very precise as he's able to pan out the speed he would need to get in Sai's butthole.