Eldritch Guidance - Chapter 8: Meeting under Cait

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

She is a two-faced and fierce hidden ghost doctor,

Ronnie, a college student with a boring life has everything around him change when his whole world is turned upside down by a woman he accidentally summons while trying to summon a magical familiar as a game.His peaceful and tranquil days are disrupted as he tries to help her fit into human society while also searching for a way to break their bond.Hell further breaks loose when he discovers that his familiar is indeed the demon queen and mysterious forces start trying to eliminate him for reasons unknown.He struggles to protect himself, adjusting to having a demon queen in his life, and understanding his growing feelings for her.