As a child, she would often get into trouble by beating people up. When she was in the fifth grade some monks captured her and did a ritual that sealed her rough personality with the chain of Sanzo Hoshi. From then on to those close to her, her sealed personality when her hair is bounded by the chain became known as "White Yui" due to her hair and the clothes she owns that she wears becoming white and when she is unbounded when her hair is let loose from the chain, she is known as "Black Yui" due to her hair and the clothes that she owns and that she wears becoming black.