Using entries to cultivate immortality in chaotic times - Chapter 16 "Isn’t She a Geisha?

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

[Complete your story by challenging countless monsters, demons, and legends]

This is the last sentence I saw before I lost my mind.

And it’s one sentence that I’m still holding on to.

That’s how the journey of killing monsters and wandering in search of all kinds of rumours began.

And it will continue.

Until the day I get out of this damn game.

A master assassin transmigrates into an interstellar era.