Miabel

Goes by "Bel". Bel's introduced by Mia as her younger half-sister. Her first appearance was during Mia's second year at Saint-Noel Academy (Volume 3 of the LN).

~!Bel is Mia's granddaughter who came from an alternative timeline future in which Mia avoided her fate of being executed by guillotine. Suddenly appearing at Saint-Noel Academy in front of Mia, she announces that Mia will be assassinated in the future and the Tearmoon Empire will be destroyed.

By the way, the name "Miabel" was given by the future Mia, and Bel really likes it as "an important name given to her by her respected grandmother", but it is actually just a simple thing to stick the names of her grandparents (Mia and Abel). When Mia realized the truth, Mia was dumbfounded by this cheap name.!~