I've already become a Hogwarts professor, and the system only just appeared.

To escape the Death Eaters, Su Yu fled from England to the United States more than ten years ago, where he made a name for himself thanks to his talent in alchemy.
He thought his life would be just an ordinary one as an alchemist, but a letter of offer from Hogwarts shattered his peaceful existence.
Along with the letter came a system, but something was amiss. Why did the system insist that what I had was a teaching appointment letter was an acceptance letter?