Mukai Kohinata

was a Konohagakure jōnin and Anbu who came from a family that was distantly related to the Hyūga clan. It was soon realised that Mukai also was a suspected spy for Kirigakure.

Itachi Shinden: Book of Bright Light
Danzō Shimura had ordered for one of Mukai's team-mates injured so Itachi could be the "fill-in" for the team. Their mission was to spy on Kiri and Sunagakure shinobi as they were appearing to be forming an alliance. Before the mission, however, Mukai went out drinking and smoking and compromised the mission. While being chased by the Suna shinobi, Mukai revealed he actually had the ability to awaken the Byakugan in his left eye and defeated the twenty shinobi.

Personality
Mukai was a smoker as well as an alcoholic and would indulge in these vices even before important missions. Despite this, Mukai was a capable ninja and confident in his abilities, willing to compromise the mission, wanting to display his abilities for the famed Itachi Uchiha. In battle, Mukai showed that he could be merciless, attacking the leader with a full Eight Trigrams technique, despite the fact that a single blow would have sufficed, not wanting to let the leader of the enemy team return unscathed.

Abilities
Mukai was an extremely powerful and experienced shinobi, capable of nearly defeating both Itachi Uchiha and Shisui Uchiha at the same time despite them both being famous prodigies in the Uchiha Clan. Indeed, he was even prepared for the Sharingan's visual prowess, and the minute he's put in a genjutsu he programmed himself to commit suicide to deprive the Uchiha prodigies from gaining any of his secrets.

Byakugan
Being distantly related to the Hyūga clan, Mukai was able to find a way to activate the Byakugan in his left eye as a genetic throwback. The Byakugan grants Mukai penetrative vision in a near-360° around himself, as well as giving him the ability to see the Chakra Pathway System. He's also shown great skill in reading the flow of chakra, even within jutsu such as the Fire Release: Great Fireball Technique; and can use this insight to split a jutsu apart.

Taijutsu
Mukai was hailed as a taijutsu expert appearing to use a variation of Gentle Fist. His skill in taijutsu was exceptional, and Mukai was capable of defeating twenty Sunagakure shinobi — all armed — without so much as a scratch, using nothing but taijutsu and his Byakugan. Itachi and Shisui, both shinobi known for their physical prowess, were unable to defeat Mukai in taijutsu and were nearly defeated in return despite them working together. His proficiency in the art of the Gentle Fist allowed Mukai to used a halved version of the Eight Trigrams Thirty-Two Palms — the Eight Trigrams Sixteen Palms.

Trivia

 * literally means "small sunny place" and "mukai", when written as "向い", means "facing".
 * Reversing the kanji of, one gets 向日, which can be read as "mukai".