Rei

Rei ("Ray" in Viz's English manga) is the successor of Nanto Suichouken, which is said to be the most elegant of the Nanto Seiken styles. He represents the "Star of Justice". Rei is introduced in the manga as a ruthless chauvinistic mercenary-for-hire of shifting allegiance whose sole purpose is to kill "the man with seven scars," whom he believes was responsible for kidnapping his sister Airi. Rei is hired alongside Kenshiro by Mamiya to protect her village against the Fang Clan. After Airi is found and rescued by Ken, Rei becomes Kenshiro's closest ally and supports him for a few story arcs.

(Source: Wikipedia)