MTL - Soaring the Heavens - Chapter 34 Changfeng

Shuu is a member of the literary club that can’t write. One day, he gets a mysterious message on his phone from a girl called Eina, and from that impulsive contact, they begin to exchange messages. They talk of things like their shared interest in novels and grow close. However, when they try and meet, they discover a shocking truth. Eina lives… not in the present, but five years in the past! How will their love develop, parted by five years of nights…!?

Mechanics fix things.Fighters break ‘em.Those were the two truths Perry lived back on Earth. When he got isekai’d into a young noble with newfound magical powers, he found himself stuck with an awful choice. Try to survive on the Front, the mystical battleground where Hydras and Devils roamed free… Or find another way.So he took an oath. An oath that made him a Magus Dominus. A mage lord. He’d escaped his fate, least for the moment.For most his life, Perry was used to being alone. When he got sucked into Ro'an, he was suddenly thrust into the role of surrogate son to his loyal servant and half-brother to a tempestuous Storm mage. With their help, Perry prepared his best to be lord and protector for his domain. And if he fought a few monsters, and helped a few people along the way, well…Mechanics fix things. And fighters break ‘em.-Progression Fantasy with light LitRPG elements-No romance-Kingdom building and magic progression

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

Within the Immortal Realm, there were nine thousand major realms, with three thousand at the top, three thousand in the middle, and three thousand at the bottom, along with countless minor realms.