A mortal woman, she was the descendant of the 18th century samurai, Hideo Koto who was the friend and martial arts teacher to Duncan MacLeod. Their association led the samurai's shogun demanding his death, MacLeod served as his second, striking off his head before he could shame himself by crying out. As a result of their friendship, MacLeod promised any of his decedents could ask MacLeod for help at any time.
After Midori watched her husband kill her lover, Akira, she stabbed him and fled seeking Duncan's help. When she presented him with a brass spy glass, he recognized it and said, "Your family name must be Koto...the Kotos can always come to the MacLeods for help." She then told him she had murdered her husband. When she returned to her hotel, however, her husband was there, and she panicked. MacLeod recognized her husband as another immortal and assured her he would not let her come to harm, and got her away from the hotel.
She told MacLeod that when her family could not repay the massive debts they owed Michael Kent, she married him, but that he did not love, he possessed, and she hated being a possession. MacLeod tried to mediate between Kent and Midori, informing Kent that if anything happened to her, MacLeod would have to kill him. Midori, however, left him the spyglass and ran, releasing MacLeod from his vow to Hideo. MacLeod followed her back to Japan, to Hideo's shrine. She told him "I chose this destiny, I have to live with it. What happens to me isn't important."
When MacLeod chose to fight Kent, she tried to stop him, saying she had released him from the vow. He told she could not, the vow was not made to her. With both men intractable as to their positions, it came down to the challenge, and Kent lost, leaving Midori the widow of a very wealthy man. "How can I thank someone for giving me back my life?"
Tamlyn Tomita also portrayed Maia Koto in the same episode.