Blood on the Tracks volume 7-10

Seiichi Osabe is a shy middle school student living a relatively ordinary life. His mother, Seiko, is considered overprotective of him by others, although Seiichi is comfortable with the love and care from his mother and does not feel anything strange about her behavior. One day, Seiichi goes on a family hiking trip with his parents and paternal family. At one point, Seiichi's cousin, Shigeru, jokingly pushes Seiichi near a cliff edge, leading Seiko to quickly grab hold of Seiichi, protecting him from falling. The rest of the family starts laughing at Seiko over her "overprotective" act. A while later, Seiichi and Shigeru go to a higher cliff edge, and when Shigeru is on the cliff edge, Seiko, who was following them, approaches her nephew and pushes him off the cliff, giving a brief smile to her son. After the incident, where Shigeru is left in a comatose state and Seiichi was the only witness of what happened, he begins to discover how dangerous his mother's affection can become, and