Seira Mimori is a thirteen-year-old student at St. Paulia's Private School and a nun-in-training at the school's church. Classmate and best friend of Meimi Haneoka, she is the only person who knows the real identity of Saint Tail. After school Seira spends her time at the chapel as a nun; many people come to her and talk about their problems, usually involving something being stolen or going missing. She relays this information to Meimi/Saint Tail, asking her to help these people recover their valued possessions. She can also help Meimi/Saint Tail when is in Trouble.