(Harry Potter fan fiction, no System, scheming protagonist, ruthless and decisive, Dark Lord, Western fantasy. Read at your own discretion.)
(Be sure to read the synopsis before you start! This novel has few comedic elements. It mainly focuses on the protagonist's calm, calculating, ruthless nature. The early part is a period of growth and preparation; later, he starts crushing his enemies. If that's not for you, proceed with caution.)
After a great battle in the Immortal Realm, a demonic cultivator powerhouse blew himself up and died. He transmigrated to the Harry Potter world with the treasured Dragon Abyss Stone, where both his magic and cultivation advanced.
"Are you really a first-year? You're so good at magic," the professors always asked.
"How can you cast Wandless Magic already? You're only a first-year!"
"Aren't you supposed to be a good guy? How did Voldemort become your lackey?"
Starting at Hogwarts, he made his plans early and stopped at nothing.
Becoming a Dark Lord or killing the various Dark Lords were simply means to an end.
His goal was nothing less than "immortality."
I finished watching it all in one go, and overall I felt it was pretty good. I hope to keep watching until the end. Speaking of which, I wonder if the main characters have a romantic partner. If they don't, then I'll definitely keep watching. If they do, I wonder if the author's writing skills are good enough to make the romance compelling. If they are, then maybe I'll continue watching.