Wortenia Senki (WN) - Volume 2 Chapter 4 (The despair of those who are being summoned 4)

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 fiancée has betrayed, but how could she know that the man she looked down upon was in fact a prodigy with healing and martial prowess!

Greed, envy, anger, gluttony, lust, sloth, prideThe 'Black Book' records seven sources of sin, which are also seven steps to ascend to godhoodOnce, I thought there would always be one sin suitable for meBut I never expectedEvery volume of the twelve military letters bears my name!

An ordinary office clerk was accidentally reborn into a vast and mysterious world of Xianxia, becoming a member of a small cultivation clan.The story begins in an endless sea of sand, in an oasis called the Yuquan Lake Oasis.