Dr. Amakasu works as a new doctor at a hospital in northern Hokkaido. He becomes the primary physician for Karin Shiraishi, a patient with pneumothorax who refuses vital surgery, haunted by her father's death during an operation. His blunt assessment of Karin as spoiled provokes her anger and leads her to vent about him online.

Seeking to expand Karin's world beyond the hospital walls, he indirectly exposes her to the outside. Though not responsible for the anonymous, encouraging emails Karin receives—which include photographs of Hokkaido locations mirroring her dreams—he owns identical photos in his office. This coincidence leads Karin to mistakenly believe he sent the messages, fueling her attachment to the unknown sender.

He shares a personal connection with Nurse Yuki, a colleague and former high school acquaintance. Nurse Yuki later reveals she authored the emails to support Karin, hoping to build a bond and persuade her towards surgery. Dr. Amakasu’s consistently firm medical guidance helps Karin confront her reality. After her brother Mitsuru collapses from overwork due to her medical expenses, Karin consents to the surgery, stipulating Dr. Amakasu must perform it—signaling her acceptance of his care despite their conflicts.

Throughout, his role centers on persistent advocacy for Karin’s health, supporting her decision to face her fears for her well-being and family.