Shunta Amanokawa, the mischievous younger brother of Sayako Amanokawa, delights in teasing his sister and displays keen curiosity about her life. This curiosity drives him to secretly follow Sayako to the Sonen Group headquarters, aiming to snap a scoop with his camera. During this escapade, antagonist Tousaku Arai orchestrates Shunta's demonic possession, resulting in a severe illness that baffles his doctor father, rendering conventional medicine useless. Taiyou Sorano intervenes, performing an exorcism to expel the demon and save Shunta. Following his recovery, Shunta celebrates by attending a summer festival with Sayako and her boyfriend, Yuki. He later joins the effort to expose Arai's conspiracy, actively supporting his sister during the climax. The narrative reveals Shunta, alongside Sayako, Yuki, and other TSI members, is a reincarnation of one of Buddha's disciples from 2,500 years ago. After the main conflict resolves, Shunta remains with his family while Sayako moves out to live with Yuki.