What's Wrong With Hogwarts Professors Knowing Dark Arts?

Lin Du, an Eastern wizard in the HP world, has always sought nothing more than to quietly research the origin of magic -- even if his research subject is the dark arts, feared by the entire wizarding world. To explore the roots of Eastern and Western magic, he sneaks into the restricted section to copy ancient texts, obsessed with the origin of the Unforgivable Curses and the possibility of reversing them. However, he is chased by the Ministry of Magic's Aurors and forced to hide everywhere under the charge of "researching dark arts." But who would have thought that his pursuer wouldn't be the guards of Azkaban, but the legendary Headmaster of Hogwarts? After a magical confrontation, Dumbledore looks at this powerful, dangerous researcher who, despite his research, adheres to his principles. He smiles and offers him a contract: "Mr. Lin, the position of Defense Against the Dark Arts Professor is yours for the taking."

Lin Du is stunned: One second he was discussing whether the Killing Curse could be reversed, and the next he's a professor at Hogwarts? He knows this is a "one-year-and-out" high-risk position!

On one hand, there's Voldemort's covert scheming; on the other, the Ministry's constant surveillance. He also has to teach a group of rebellious young wizards -- but the upside is that he can continue his research within the framework of Hogwarts, with Professor McGonagall's covert support.

Lin Du looks at the mess before him and silently grips his wand: Fine, isn't it just about surviving one term? As a "king of cramming" professor from the East, can't he handle this little situation?