Shin Kuroi Kaze

(from ebookjapan):
Kaze is a lonely boy who is extremely skilled with a sword, but is ruthless and cruel in slaying those who try to kill him. One day, he decides to go on a trip with Chibi, whom he met by chance. Chibi calls Kaze "Aniki," which means "big brother. However, along the way, dangerous opponents target Kaze one after another. Kaze is chased by a twin named MURAJI. With the word "revenge" in their hearts, Kaze and Chibi's journey continues today... A ninja action drama set in the turbulent days at the end of the Edo period.