Rurouni Kenshin: Trust & Betrayal

While a raid of bandits slay a group of travelers, a young boy named Shinta is saved from death by a passing swordsman. The swordsman, known as Hiko Seijūrō, is a master of the Hiten Mitsurugi, the strongest of all sword forms. After seeing the boy bury the bodies of not only the travelers but also the bandits, Hiko is impressed and takes Shinta as an apprentice, renaming him "Himura Kenshin", a name which he felt was more appropriate for a swordsman.

Note: This is the 1999 OVA, not the movie from 2003