Rainbow

The year, 1955. Six delinquents nicknamed Mario, Cabbage, Soldier, Turtle, Uncovered, and Joe are taken to a prison-like reform school due to their various crimes. They are introduced to Dr. Sasaki, the school physician, who performs a painful rectal exam on each boy. Humiliated, they are led to their cell-like room, where they met a boy named Sakuragi. Mario starts a fight with Sakuragi, culminating in Sakuragi knocking out all six boys. Ishihara, the school's sadistic head guard, violently beats Sakuragi as punishment while the others watch. Later after Sakuragi regains consciousness, he accepts a stashed cigarette from Joe, then proceeds to share it with the others. Sakuragi's strong, yet benevolent actions immediately earns him the respect and admiration of the six boys.

The seven boys have become comrades and spend time working out in their cell. Joe reveals that he has a younger sister on the outside. Seeing her again is his sole motivation to endure the school. Joe later receives a visit from the orphanage administrator where his sister is staying saying his sister is about to be adopted. Afraid he will not see her again, Sakuragi and the other boys cause a distraction allowing Joe to escape through an unguarded entrance. The boys are beaten and placed in solitary confinement. Turtle recounts losing his entire family in the atomic bombing of Hiroshima and why he helped Joe escape. Joe arrives at the orphanage and attempts to escape with his sister but is caught by the police. Joe's sister 'rejects' him and sends him away (in an attempt to protect him). Distraught, Joe is returned to the school and placed in solitary.

Joe leaves solitary and Sakuragi's words are able to comfort him. Joe resolves to survive and one day reunite with his sister. Ishihara tells Uncovered that Sakuragi murdered his parents. Uncovered confronts Sakuragi in the mess hall, resulting in the two almost coming to blows. Sakuragi is taken and beaten by Ishihara who greatly hates Sakuragi for being the lone student in the school who is not afraid of him. Uncovered remembers his early childhood being poor and how his mother was sexually exploited to get food, causing him to develop a distrust in others. Ishihara discovers Uncovered with a stash of hidden cigarettes. Using Uncovered's fear of him, Ishihara schemes to implicate Sakuragi. A fire, ignited by one of Uncovered's tossed cigarettes, causes an evacuation of the cells. Uncovered is horrified when Ishihara purposely throws away the key to Cell 6, in an attempt to kill Sakuragi. Sakuragi confronts Uncovered outside and learns the other boys are trapped in the burning building and rushes back inside in an attempt to save them.

Uncovered can't believe Sakuragi would risk his own life for someone else, believing that you can only rely on yourself. Sakuragi arrives at the cell, but can't open the door. The building begins to collapse and Sakuragi is knocked down by flaming debris. Outside, Uncovered searches for the lost cell key and locates its. Ishihara arrives and demands the key but Uncovered refuses to give it up. Uncovered enters the building and saves Sakuragi and the others. They escape and then Sakuragi knocks out the shocked Ishihara. Sakuragi is taken to the hospital to recover from his injuries. He tells a nurse about how he greatly admired his father, a soldier. However, after the war, his father returned home a broken man. One night, Sakuragi confronted his father saying he had lost all respect for him. A short time later, Sakuragi's father commits suicide. Sakuragi believes he 'murdered' his father, because he didn't try to understand his father's pain and believes his hurtful words drove his father to kill himself. Sakuragi doesn't want to lose anyone else important to him and that the other boys are his best friends. Overhearing this story, the bond between the seven becomes even stronger.

After leaving the hospital, Sakuragi reunites with his cellmates. A new guard, Kumagai, has replaced Ishihara who is on house arrest related to the fire. While doing community service outside one day, the boys each relate their dreams. Before returning to the school, the boys carve their dreams into a large tree and promise to meet back at the spot after they get out of the school. Ishihara returns and conspires to with Dr. Sasaki to deal with Sakuragi, who will be released in a month. They remove Sakuragi from cell 2-6 and place him in another cell with several large, strong boys. They beat him nightly, yet Sakuragi continues to bear the pain and smile, frustrating them. Mario, learning of the beatings, begs to take Sakuragi place in exchange for them sparing him. They beat Mario and shatter his right hand with a large stone. That night, the bullies taunt Sakuragi with what they did to Mario. After hearing they shattered Mario's hand, Sakuragi pulverizes the ringleader's face with a single punch. The other bullies stare in shock as Sakuragi's tells them that he was willing to put up with their abuse, but that they crossed the line when they attacked his friend.

The other bullies attack Sakuragi, while Ishihara listens from outside the cell. Ishihara leaves content that Sakuragi will be bludgeoned to death by morning. In the morning, Ishihara opens the cell, but is horrified to see all the bullies beaten and bloody on the floor. Cowed by the beating they suffered, none of the bullies are willing to admit it was Sakuragi's fault, causing Ishihara to leave in a rage. Unable to intimidate Sakuragi, Dr. Sasaki suggests Ishihara make Sakuragi break the rules by hurting his friends. Realizing Ishihara's goal, the boys bear the abuse to protect Sakuragi. Sakuragi, no longer able to watch, grabs Ishihara and is in turn placed in solitary confinement. Ishihara plans to starve Sakuragi to death saying that he and Sasaki can't let him out because of what he knows. One year earlier, Sakuragi had a roommate named Ei'ichi who was sexually molested by Dr. Sasaki. Unable to live with the constant abuse, Ei'ichi committed suicide. Guard Kumagai reveals Ishihara's plans to the boys in 2-6. Turtle manages to sneak food to Sakuragi's cell, restoring his will to survive.