Sonomiya-san no Muko Jijou

Junrei, the daughter of the Sonomiya family, is living with Chika, a student from another school, for only a month. She thinks Junrei is meeting her for the first time, but Chika is actually the boy Junrei made a promise to be her groom when she was little! As they learn about each other's emotional scars and reach out to each other, the distance between them gradually closes. But when Junrei doesn't remember her "promise," the time comes that they may have to say goodbye!

(Source: Libre, translated)