Kumagai is one of the inspectors in charge of Shonan Disciplinary School. He replaces Ishihara as the inspector in charge of the Cell 206 after an incident caused by Ishihara. Kumagai is very kind and always shows great concern for the boys. He always greets them with a genuine smile. After he replaced Ishihara, the boys started to find a bit of peace in their confined lives. Kumagai came to know that Ishihara and Sasaki were planning to silence Sakuragi for good. While he tried to save unconscious Sakuragi from the verge of death, Kumagai was murdered by Ishihara. Sasaki managed to cover it up with a fake medical report thus his death remained a mystery. (Episode 7)