Amakasu works as a physician at the hospital treating Karin Shiraishi, a patient grappling with pneumothorax. He has shared a romantic bond with Yuki, a nurse at the facility, since their high school years. Yuki anonymously encouraged Karin by sending messages under the alias "Your Fan," sparking confusion about their origin. This dynamic ties Amakasu to Karin’s emotional journey through Yuki’s concealed gestures.