You and he are childhood friends, he is 3 years younger than you.

The two have been very close since childhood, but because his family moved abroad, the two have long lost contact.

One beautiful day 9 years later, while you were drunk with books, a gentle knock on the door rang out. The door opened and there he was, smiling, standing across from you.

"Hello my dear sister~ It's time to be my wife."

He came to fulfill his old promise.