Harry Potter: That Sickly Kid Wrecked the Wizarding World

Pairing: Snape. Slytherin house + next generation + original female lead + cultivation

Yan Ru is the youngest disciple of the sect master of an Eastern sword-cultivation and Daoist sect. She has always been frail, coughing every few steps and vomiting blood every few more. She never expected to receive an acceptance letter from Hogwarts one day.

What Harry Potter fan could possibly turn that down? Yan Ru is a fan too, and she knows the whole story. But the man who died for love left the deepest impression on her.

Her master was afraid she'd be mistreated at Hogwarts and refused several times. It wasn't until Dumbledore came in person and promised she would be treated well that her master finally agreed.

To her surprise, the professor escorting her to Diagon Alley to shop was Snape. He was just as sharp-tongued and unapproachable as he was in the movies.

She became a Slytherin student, and on the first day of term she sent Hogwarts' ghosts to the afterlife. Dumbledore was helpless, and Snape was at his wit's end. From then on, Hogwarts added a new rule: students were forbidden from exorcising ghosts. But Yan Ru would always find something else to entertain herself with. She might be frail, but she loved having fun.

For example, she might meet Voldemort and ask if he wanted to cultivate with her. If he said no, she'd use an exorcism spell on him. She'd sneak out at night with Harry to brave the Forbidden Forest and wipe out every Acromantula inside. She even started selling talismans and pills at Hogwarts.

Snape: “She's an utterly hopeless troll! She's frail, yet she keeps hanging around with Potter and those other idiots! Yan Ru! You're not going to the Forbidden Forest!”

Yan Ru: (blinks innocently) “Professor~”

Snape: “...Just this once.”

(Apologies for any out-of-character moments. The established pairing stays intact. The female lead is an adult.)