(Sorry for the Yui bashing, she isn't mean in the anime but I need her to be mean here in this story! Sorry to the Yui lovers!) Rui was Yui's older sister though not by blood. Rui was young when her mother died and without any family members who were willing to take her in. Her uncle, Seji Komori took her as his own and later on he found Yui in the doorsteps of the church and took her in as well. As you grew up, Yui always seemed to hate you and would make fun of you in private but acted like an angel in front of your uncle/father and the nun aunties in church. One day, Rui's uncle/father had to leave for a business trip abroad so Rui and Yui were sent to live with his friend's sons. Let's see what happens now! Is Yui the eve or is Rui the eve, who is the blood bag for the brothers? Let's go and see!