MTL - Godly Thief Incarnation - Chapter 73 Amazon’s former overlord - Mori

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

The strongest Demon Lord dies, and reincarnates as a human. Not only that, he because of various incidents turns into the hero’s best friend.

Follow his journey as he tries to help the hero escape his fate, and on the sideline to conquer the continent while he’s at it.

[Congratulations! You’ve unlocked the Dimensional Motel System.][First Mission: A runaway princess—hailed as the most beautiful in the land is being hunted by her step-mother. She was originally headed to the dwarves’ cottage, but the System has rerouted her to your motel instead.][Protect her. Win her trust. And if you manage to woe her, you’ll earn her Affection Points.][Bonus Mission: Sleep with her evil stepmother to unlock more reward]'What kind of weird mission is this? And why does this story sound way too familiar?'

“Future Occupation…Demon King.”

Sai Akuto enters Constant Magic Academy to be useful to society and to become a top-ranked national magician. However, a horrible prediction is made on his first day. Thanks to this prediction, the class representative girl hates him, a girl with a mysterious power embraces him, a female artificial human is sent by the empire to observe him, and his school life is otherwise thrown into chaos…