Monster (Japanese: 怪物, romanized: Kaibutsu) is a 2023 Japanese psychological dramatic mystery thriller film directed and edited by Hirokazu Kore-eda from a screenplay written by Yuji Sakamoto.^[4] It stars Sakura Andō as a mother who confronts a teacher after noticing disturbing changes in her son's behavior.^[5] The film marks the first time Kore-eda has directed a film he did not write himself since Maborosi (1995). The film was the last scoring project by Ryuichi Sakamoto (no relation to Yuji Sakamoto), who died two months before its release; the film is dedicated to his memory.^[6]

Monster had its world premiere at the 76th Cannes Film Festival on 17 May 2023, where it competed for the Palme d'Or and was honored with the Queer Palm as well as the Best Screenplay award. The film was released in Japan on 2 June 2023. It received widespread critical acclaim with special praise for its screenplay, direction, acting, editing and musical score and appeared in many lists of top ten year's best.

Saori Mugino is a single mother raising her fifth grade son, Minato. He soon begins exhibiting strange behavior such as cutting his own hair and coming home with only one shoe. One night, Minato does not come home at all and after calling around, Saori finds him in an abandoned train tunnel. Saori begins to suspect her son's teacher, Mr. Hori, is abusing him and confronts the school about it. She is treated coldly by the faculty, culminating in Mr. Hori making a disingenuous apology. When she confronts Hori directly, he asserts that Minato is actually bullying another student named Yori. Saori visits Yori's house and he, despite his own strange behavior, seems fond of and concerned for Minato. Hori is eventually fired from the school, but returns days later and Minato falls down a flight of stairs trying to escape from him. Hori later comes to Saori and Minato's house during a rain storm, but Saori finds that Minato has gone missing.

A flashback returns to the beginning of the film from Hori's point of view. He notices Minato exhibiting disruptive behavior, such as throwing other students' belongings around the classroom and seemingly locking Yori in a bathroom stall. Hori too visits Yori's house, where he discovers that his father, Kiyotaka, is an abusive alcoholic. When Saori begins inquiring about her son, the faculty pressure Hori to let them handle it to protect the reputation of the school, ultimately requiring him to resign. After he is hounded by journalists and left by his girlfriend, Hori returns to the school to confront Minato, and contemplates jumping from the roof of the school after the boy falls down the stairs. During the rainstorm, Hori notices a pattern in Yori's old homework that seems to spell out Minato's name. Realizing the two boys were actually in love, Hori rushes to the Mugino household to apologize and assure him nothing is wrong with him. When Saori tells him Minato is missing, they go to the train tunnel to find him. They find an abandoned railcar nearly buried in mud, but inside the train car, we only see Minato's poncho.

A final flashback begins from Minato's point of view. Yori is routinely picked on by the other boys for his asocial and seemingly effeminate behavior. Yori plays with Minato's hair, which the latter then impulsively cuts off. The two boys grow close and Minato begins defending him from other bullies, which Hori confuses for bullying. As the two become closer, Minato is distressed that his feelings are becoming romantic and that he is not a worthy son to his father. One night when he goes to Yori's house, Yori and Kiyotaka declare that Yori has been "cured," though Yori quickly recants, which incites his father's wrath. During the rainstorm, Minato finds Yori abandoned fully clothed in his bathtub, covered in bruises, and the two escape to the abandoned railcar, which has become their hideout. After the rain subsides, they emerge from the bottom of the railcar and question whether they have been reborn, and run through a field together. In the distance, a path the two wanted to take earlier that was gated off is now gate free, with no wreckage in sight.

• Sakura Andō as Saori Mugino, a single mother
• Eita Nagayama as Michitoshi Hori, Minato and Yori's homeroom teacher
• Sōya Kurokawa as Minato Mugino, Saori's son
• Hinata Hiiragi as Yori Hoshikawa, Minato's classmate
• Mitsuki Takahata as Hirona Suzumura, Hori's lover
• Akihiro Tsunoda as Humiaki Shoda, the vice-principal of the elementary school that Minato and Yori attend
• Shidō Nakamura as Kiyotaka Hoshikawa, Yori's father and a single father
• Yūko Tanaka as Makiko Fushimi, elementary school principal

A teaser trailer was published in early January 2023.^[19] A promo was shown in February 2023 at Berlinale's European Film Market.^[11] Monster was selected to compete for the Palme d'Or at the 2023 Cannes Film Festival,^[20] where it had its world premiere on 17 May 2023.^[21] It was also invited at the 28th Busan International Film Festival in 'Gala Presentation' section and was screened on 7 October 2023.^[22]

In Japan, the film was released on 2 June 2023, co-distributed by Gaga Corporation and Toho.^[23] Gaga has the distribution rights for the rest of Asia. Goodfellas will handle international sales excluding Asia.^[24] Well Go USA Entertainment acquired the U.S. distribution rights and gave the film a limited theatrical release beginning 22 November 2023 in New York, followed by December 1 in Los Angeles, before expanding wide on 15 December.^[25][26][27] Nathan Studios distributed the film in the Philippines and was theatrically released on 11 October 2023.^[28][29]