Rika was adopted by Rintaro at a very young age after her parents had passed away in a car accident. After she was adopted she met her new sister Ema and promised to always protect her so that Ema would always be innocent and happy. Rika excelled in school so the principal suggested she go to a boarding school in France because they had nothing else to teach her. Though Rika was sad to leave her sister she had to go because the school would no longer teach her and Rintaro wanted her to get a good education. Now Rika's 15 and ready to come home after she heard that Rintaro was getting married and that Ema would be staying with their new stepbrothers.
Now that Rika's coming home what will happen will the boys fall for her instead of Ema or will they just be brothers and sisters.
Find out in this story of The Secret Sister.