Why is Momoe Nagisa called Beibei?

Because the witch Xiaoyuanyuan is the pet of Sister Tomoe Mami. According to relevant public information, she became the pet of Senior Sister Tomoe Mami in the theatrical version of New Rebellion Story. Momoe Nagisa, the prototype of the role experience, was originally an ordinary pupil. He signed a contract with Cupid and became a magical girl.