Confessions (Kokuhaku) 2010 movie

Yuko Moriguchi (Takako Matsu), a junior high teacher, announces she will resign. She reveals that her daughter, Manami, was killed by two pupils in her class, whom she dubs "Student A" and "Student B". Her disclosure of their behavior soon reveals their identities, but she recognizes that they will escape punishment as legal minors. Instead, she admits to injecting her dead husband's HIV contaminated blood into the milk cartons that the murderers have just drank from. The rest of the film describes the aftermath of this event in a series of first-person narratives from the two students, Moriguchi, and others.
A new enthusiastic teacher is appointed. Student A, Shuya Watanabe, continues to attend classes but student B, Naoki Shimomura, has developedpsychiatric problems. It is revealed that Shuya, who planned the murder, did not actually kill Moriguchi's daughter by electrocution; instead she drownedbecause Naoki threw her into the pool.

Naoki is worried that he will soon die from AIDS and refuses to clean himself, as he equated the smell of untamed hair and body odor to being alive. His mom tries to help but fails as Student B reacts violently to her gestures and shuts himself in his room. It is revealed later that Student B killed Manami on purpose, as a gesture to validate himself in the eyes of Shuya, whom he considers his only friend. His mother eventually realizes that her once good and kind son has transformed into an unknown monster. Seeing no hope, she decides to end their lives, but in the ensuing struggle, she is killed by her son, who is captured by the police.
Shuya describes how his mother divorced his father when he was young because she was unhappy with the role of a house wife and chose instead to pursue her scientific ambitions. He wants to prove himself to her and to earn her attention, which evolved from clever little inventions to gruesome recordings of him killing and dissecting animals. His first public invention, an electric anti-mugger wallet, earns him a science fair award but fails to make the headlines because of a sensational murder that occurs on the same day. He decides to kill someone so that he can become front page news.After the incident, Shuya befriends Mizuki Kitahara when they were forced to kiss by the rest of the class as part of their escalating bullying tactics against him. Mizuki discovers that Moriguchi had lied about the blood-contaminated milk, reasoning that it was an implausible method of revenge to begin with and that someone so concerned with the value of life would not do such a thing in the first place. Mizuki begins to develop feelings for Shuya, revealing to him a side of herself she'd never shown to anyone else: namely, that she sees Lunacy, the online handle of a teenage girl who killed her parents in a sensational poisoning incident, as her "other self." When she confronts Shuya for not facing his mother and harboring an Oedipus Complex, Shuya kills her out of rage.
At graduation, Shuya plants a bomb to kill himself and his classmates, but the bomb does not go off and is revealed to be missing; he then receives a call from Moriguchi telling him she had moved the bomb to his mother's office, killing her instead. Moriguchi appears at the end, and tells Shuya, overcome and humiliated, that this was her revenge, and that his redemption now begins, but she adds, "just kidding", referencing to what Shuya told her when he confessed that he killed her daughter.