Komori Yui is a normal girl who gets sent, by her father, to the Sakamaki brothers' house. She is a good-natured and sweet girl. She is also strong despite the horrible situation she is in and everything. Her dad works in a Church and she has the power to see ghosts.
It was Ayato who gave her the nick name "Pancake," referring to her flat chest. In season 2, the Mukami would either call her Sow or Live stock for most of the time.