Tajomaru (2009)

Naomitsu is the second son of the Hatakeyama family and fiance of Princess Ako. When he gets chased away from his home as the result of a conspiracy against him, Naomitsu flees into the mountains with Ako in tow, but they're soon attacked by a bandit named Tajomaru. After managing to kill Tajomaru, Naomitsu takes the bandit's identity as his own.