An old woman (Nobuko Otowa) and her daughter in law (Jitsuko Yoshimura) are trying to survive in feudal countryside of Japan in the 15th century. The only way they can make money is by killing lost samurai and selling their belongings to a fence named Ushi (Taiji Tonoyama). The two women kill their pray in the tall susuki reeds that surround their hut. After killing and stealing the belongings of the samurai, they pull their bodies to a deep dark hole and they dump them down into it.
The old woman’s son has gone off to war and since they are all alone, they must do whatever they can to survive. One day, her son’s friend Hachi (Kei Sato) comes home to the susuki fields and comes to the home of the old woman. She wants to know where her son is, but sadly he has died in the war,. The old woman is very upset, because she suspects that Hachi left her son to die. While at the home, Hachi discovers the daughter in law who’s now alone since her husband has died.
Hachi starts to hang around the hut each day and its obvious he wants to be more than just friends with the young woman. One day while fishing, Hachi spots two warriors who are battling in the water. The old woman and daughter are on the shore nearby washing their clothes. Hachi kills one of the warriors and the old woman and daughter in law kill the other. They sell their belongings to Ushi and take their bodies to the hole.
Meanwhile Hachi is looking for love from the daughter in law and the old woman doesn’t like it. Hachi follows her and makes his feelings known that he wants to be with her. One night, the daughter in law runs out to Hachi’s hut, she gets very scared running through the susuki reeds at night. But she gets to Hachi’s hut and they proceed to make love. The old woman wakes up one night and realizes that her daughter in law is secretly sneaking off to see Hachi. She is jealous and angry. She trails the daughter to Hachi’s hut and she spies on them while they are making love. In a telling scene, the old woman is extremely frustrated and she begins to hug a tall tree.
The old woman sees Hachi in the field the next day and she tries coming on to him. But he is repulsed by the old woman. He laughs at her and tells her he’s not interested in old women like her. The old woman proclaims “I might be old on the outside but I’m not old on the inside”. When Hachi refuses, the old woman warns him to stay away from the daughter in law. If not she will kill him. She tells Hachi that her daughter in law is the only reason she can keep killing the lone samurai, she can’t survive by herself. Hachi explains that he will just be friends with the daughter, nothing more.
One night after the daughter in law sneaks out, the old woman is all alone and is frightened by a large blade that sticks through the hut wall. She hides in the corner and suddenly a demon’s face appears. As the face moves closer, we see that it is in fact a lone samurai, who has lost trying to find his way to Kyoto. The old woman tells him to get out. But he needs someone to lead him to the road. She relents at first, but agrees to help him. As they are walking through the reeds, the samurai explains that he wears the demon mask to protect his beautiful face from being scarred in battle. The old woman doesn’t believe him and asks to see his face. He tells her to get going or he’ll kill her. She walks on, but then the samurai warrior falls right into the deep hole. She has set him up to die. Afterwards, she gets a rope and crawls down into the hole, it is full of skeletons of the dead samurai she’s killed. She pokes the masked samurai to see if he’s still alive, but he is in fact dead. She tells him he “deserved to die after killing all the people in the war”.
The daughter in law goes to meet Hachi the next night and as she’s running through the reeds she comes upon a figure with the same demon mask the warrior wore. Is it the ghost of the dead warrior coming back to avenge his murder?
Onibaba is based on a Buddhist bedtime tale that was told to Director Kaneto Shindo as a small child. Shindo does a wonderful job of creating both a thrilling and erotic atmosphere in the field of susuki reeds.