Mr. Kinpachi in Class 3B

Sakura Middle School management has decided to open a day care center for the elderly using vacant classrooms. Of course, the center would be run by professionals. Kinpachi's role is to provide the students with the proper information and outlook in dealing with the elderly. One day, the grade 3-B (9th grade) teacher is rushed to the hospital after being beaten up by his students. Kinpachi takes over the class while the teacher is mending.

Rikiya gets into trouble when he breaks the school windows. His reasons are unclear. He starts working at the day care center in order to pay for the damages. Of course, that means he can't attend classes, but he's not losing any sleep over it.

Atsushi, an excellent student, collapses at school for no apparent reason. Kenjiro visits him at home, feigning concern, to warn him to keep quiet about the incident with Mr. Nakano. The next day, Atsushi skips school and finds himself before Mr. Nakano's home instead...

Although Kenjiro plays the innocent in front of his teachers, he continues his pranks behind their backs. When Rikiya drops an envelope full of cash, Kenjiro hides it and watches as Rikiya searches frantically for it. Kinpachi just can't seem to get a grasp of his class.

Kinpachi's class must decide what to do for the school's Cultural Festival. Class leaders are nearing the end of their rope when the Karate Club members suggest a karate demonstration. Their advisor doesn't believe it's appropriate, but Kinpachi steps in to help.

It's finally time for the Cultural Festival. Overwhelmed by the fervor of their advisor, Mr. Endo, the unity of the students of 3B shows signs of crumbling. Kinpachi has his own problems with Endo, who shows up at the Sakamoto home in Kinpachi's absence, with a gift for Otome, his daughter.

Kinpachi gets two transfer students at the start of the second term. Although the other students try to make them feel welcome they make no headway. Kinpachi later discovers that his son Kota has collapsed on his way to school. The doctor diagnoses him with a type of leukemia. Kinpachi, who lost his wife to cancer, is devastated.

Kinpachi's heart is heavy, with two students who just won't fit in, and worry over his son, who has been hospitalized. Nao is called into the Principal's office and reprimanded for her bad attitude. Meanwhile, Masanori seems to be suffering from emotional problems too.

Nobuta has been repeatedly tardy. Kinpachi thinks he's just been oversleeping, but in reality, he has family problems. Seeing how frustrated his son is at not being allowed to leave the hospital, Kinpachi decides to tell his son the truth about his illness.

Kosaku becomes more emotionally unstable when he learns the truth about his illness. Losing his hair due to chemotherapy aggravates his emotional state. Kinpachi does his best to encourage his son, at times with strong words, at times with tender actions.

When Kinpachi takes a cap which another teacher has knitted for Kosaku to the hospital, Kosaku shows him one that a young female cancer patient has given him. For the first time in weeks, Kinpachi sees him smile.

Kosaku uses a computer to find out all he can about his cancer, so he can fight it. Meanwhile, former 3B students gather together in order to put into effect a suggestion made by Kinpachi years ago--to register at a bone marrow bank when they turned 20.