Rurouni Kenshin

This manga, serialized in Shonen Jump, tells the story of Kenshin, a man feared as the assassin Battosai during the Bakumatsu period, who vows never to kill again and seeks a way to atone for his sins while fighting enemies who lived through the same era. It's a long-running series, having been adapted into two anime series, a live-action film, and sequels to the original manga.