Shura No Toki: Age of Chaos, Vol. 1
According to legend, there was a clan of warriors in the Hiean era who were a match for any samurai even though they fought without weapons.  They were called the Mutsu clan, and their art was known as the Mutsu Enmei Style.   The great samurai, Musashi Miyamoto, cuts down a group of assassins and saves a young nobleman.  However, he has no desire to work as an escort.  To keep the young master safe, Musashi recommends a passerby from whom he senses great potential.  And thus, Yakumo Mutsu becomes a bodyguard, and the young master gains the protection of an invincible warrior.