Merupuri

High school freshman Airi Hoshina has her life goals all planned out - meet a wonderful boy, get married by age 20, and enjoy an ordinary, loving family life. However, Airi's plan breaks down when she loses an heirloom hand mirror she carries on the way to school. She finds it in the hands of a lordly little boy named Aram, who just used it as a portal from a magical world. Aram has come to Airi's world in hopes of outrunning trouble at home, but it soon becomes clear that he can no more accomplish that than he can keep Airi from getting mixed up in it.
From Viz:
All high school freshman Airi Hoshina ever wanted was to someday live in a cozy home with a loving husband, and find joy in the little things in life. As a result, she makes it her daily mission to get to school on time because school legend has it that the longer one's non-tardy streak is, the better boyfriend one will find. But just when her daily routine is working like clockwork, an occurrence of fairytale proportions threatens to disrupt her grand plan.