Miwa and Akane are childhood friends, and after graduating from high school, Miwa became a dental assistant, while Akane followed her own path, becoming a dental hygienist. Miwa and Akane have opposite personalities; while Akane is clever, assertive, and has a cruel side, Miwa is a gentle, kind, and pure girl. Miwa relies on Akane for everything, and Akane doesn't mind. Akane wants to control Miwa, and Miwa wants to obey Akane. Time passes, and one day, when the two are in their thirties, Akane is diagnosed with cancer...