Aoi and Akane Kajiya are twins who could hardly be more different. Aoi is intelligent, diligent, and well-mannered, whereas Akane is athletic, pretty, and something of an airhead. They were constantly compared in childhood, but Aoi has since become a shut-in. The divide between them has widened over the years, yet this begins to shift when Aoi returns to school. Romantica Clock chronicles the daily lives of the twins across school, everyday life, and romance. Driven by her determination never to give up, Akane will surely surpass him. Still, despite their rivalry, the family bond between them remains the strongest force.