Michiko is Wataru's wife.
Michiko and Cotton met in Japan during World War II while Cotton was stationed there with the U.S. Army. After Cotton's shins were blown off in a battle, Michiko was Cotton's nurse and spent a lot of time taking care of him. During this time, the two of them fell in love and had an affair, which resulted in the conception of Junichiro. But before either of them knew she was pregnant, Cotton was transferred back to the United States. Michiko then had Junichiro. She had a hard time raising him as a single parent, but eventually she met and married another man, Wataru, who was willing to help her. She still told her son about his father Cotton.
Cotton met Michiko again (and the rest of the family met her for the first time) in "Returning Japanese", when Cotton went to Japan for a reconciliation ceremony and the rest of the family came along. Unknown to everyone else, however, Cotton's main objective was to find Michiko. When he did, everyone met Junichiro.
Cotton and Michiko had a reunion where they each learned how the other had spent the last fifty years. She was glad to see that Cotton's feet managed to stay in place despite predicts that they wouldn't. Just before the Hills returned to the USA, Michiko ripped a picture of herself and Cotton in half. She gave Cotton the half of the picture that showed her, while keeping the half with Cotton for herself, so that each of them would have something to remember the other by. Then she gave Cotton a good-bye kiss. She has not been seen or mentioned since.
- Michiko is a common female given name with numerous meanings, including "Child Not Yet Known".
- Cotton has described her as the only woman he has ever truly loved.