Highlander S03E01 - The Samurai

After Midori Koto sees her husband, rich industrialist Michael Kent, murder her lover, Akira Yoshida, she kills Kent and runs to MacLeod for protection. She reminds MacLeod of a vow of protection his "ancestor" (actually MacLeod himself) made to her family over 200 years before. Flashbacks tell the story of MacLeod coming to the aid of the samurai Hideo Koto after being shipwrecked in Japan. Hideo befriends MacLeod - even though the penalty for helping a "barbarian" in isolationist Japan is death. When Hideo's feudal overlord forces him to commit ritual hara-kiri for that crime, MacLeod serves as his second. He vows to Hideo that he will always protect the Koto family and is bequeathed the dragon-head katana sword he uses to this day. Back in the present, MacLeod discovers that Kent is an Immortal and he's still alive. In order not to further dishonor her family's name, Midori returns to Kent. Kent challenges MacLeod, who takes Kent's head, fulfilling MacLeod's vow to the Koto family and freeing Midori from her loveless marriage.