Two sisters are engaged in a fierce battle for dominance over happiness; Keiko, a beautiful but ordinary housewife who desires a simple happy life and her younger sister Shiho, who finds the greatest pleasure from seeing Keiko unhappy. The story begins when Keiko begins to suspect her husband of infidelity due to his behavior and actions. Her best friend Yuka's cryptic warning that "The first year of marriage is dangerous" only fuels her doubts. One day, Keiko casually looks at her husband's phone and discovers a message from Yuka. Furthermore, Shiho witnesses a secret meeting between Shinichi and Yuka! Is Yuka the "other woman?!" Shocked by her friend's betrayal, Keiko starts to feel increasingly lonely. However, it turns out the true mastermind is someone else entirely - her sister Shiho had been cheating repeatedly with her husband. With Keiko finding happiness, Shiho's ugly plan to plunge her sister into the depths of despair has begun. It becomes increasingly evident that Keiko's true enemy is her younger sister. What will become of this twisted drama of a messy affair between sisters? (Source: Drama-Otaku.com)