Harry Potter: Eclipse. - Chapter 17:

Yang Gang accidentally became the imposter heir to a wealthy family, with a beautiful older sister and a twin younger sister at home...

He is a young man without a spirit root. It is believed that this denies him the chance at cultivation. However, a mysterious lady imparts a Supreme Demon Classic to him and from then on, he starts his path of cultivation.
He undergoes a total transformation to emerge as the most fearsome and powerful fiendish demon in his era, that even immortals and fiends are fearful of him, and saints are at his beck and call.
Mastering the Supreme Demon Classic is the turning point in his life. He is able to unleash his immense and divine power from within, illuminating the entire universe!

- Description from Novelupdates

Leon was once an ordinary man—until he died saving children and woke up in a new world as the last prince of the demon race. But his awakening comes with a cruel truth: the war is already over.The Demon King is dead. The once-mighty demon empire lies in ruins. And now, Leon stands amidst the ashes, surrounded by a handful of survivors teetering on the brink of extinction.Crowned Demon King by default, he holds the title—but there is no kingdom left to rule. The few remaining demons are barely surviving, hunted and outnumbered. Worse still, Leon, who once enjoyed the luxuries of modern technology, must now navigate a harsh world stuck in the Middle Ages.Can he pull the demon race out of their misery? Can he reclaim the power they once held? Or will history remember him as the last king of a fallen race?Follow Leon on his journey to rebuild, conquer, and defy fate itself.

In the mortal world, the grass and trees are in autumn, she thought she could live her own life happily, but she did not expect to shoulder the heavy responsibility of revitalizing the family.

She has a very high spiritual root value, and it is reasonable to say that she is a rare genius. However, Lei Shuimu is such a fucking spiritual root that she can electrocute herself. How should she shoulder the responsibility that the Dao has entrusted to herself?

- Description from novelbuddy