Sachiko

Sachiko is a character from Satoshi Kon's Tokyo Godfathers as well as, supposedly, being the main antagonist of the film. She is a young woman struggling with a severe mental health crisis following giving birth to her stillborn baby, and years of marital problems.

Personality
Sachiko doesn’t appear until the final act of the film. She is first seen ready to commit suicide by jumping off a bridge, but is quickly saved by Hana and Miyuki. She claims at first to be the mother of Kiyoko, but it's later discovered that she actually stole the infant from the hospital, due to a psychiatric break caused by the stillbirth of her own baby. She states that the moment Kiyoko smiled at her, she decided to take her as her own. When she's discovered, she tries running away with Kiyoko, only to be on left with a dead end on the top of a building, confronted by Miyuki. She tries jumping off the tower with Kiyoko to be reborn and start a new life all over again, only to be stopped and saved again by Miyuki and realizes what she has done to Kiyoko, cries, feels ashamed and returns her to the trio for her to be brought back to her parents. It is assumed that she will be given psychiatric treatment following her abduction of Kiyoko and later suicide attempts. It is possible she has reunited with her husband, who she had a very difficult relationship with due to his gambling and drink habits, although it is likely the property would have to be cleaned before she could return home.

While she is probably the closest thing the movie has to an actual antagonist, she really hasn't done anything to make her an actual villain, aside from stealing a baby during her mental health crisis. For a majority of her screen-time, she appears as desperate, emotional, delusional, suicidal, but changes after she recognizes her faults. It is possible that Sachiko is suffering from postpartum psychosis.

Background
Sachiko previously worked in a hostess club to pay off her husband's gambling debts, where she went by the name Midori (みどり). In the beginning it seemed that she and her husband had a close and loving relationship, however these seems to have changed over time. It's stated by her neighbours that the couple didn't keep their house clean and that they fought frequently over her husband's rising gambling debt and increasing alcoholism, as well as Sachiko being the only money earner. Unable to work due to her pregnancy, they lost their home as they could no longer afford it, leaving the house to be foreclosed and demolished.

Trivia

 * According to Sachiko, she lost her baby before it was born. As we know she was previously noticeably pregnant and was a patient on the maternity ward, it is likely that her baby was either a late term miscarriage, or stillbirth.
 * According to a Yakuza character introduced in the film, Sachiko had plastic surgery done to her before she went to work for them.