Naze Boku no Sekai wo Dare mo Oboeteinainoka? - Volume 1 Chapter 3 part1

Fate, a gatekeeper who had been working for the castle, is beset by a few burdens.

To pass as an imperial concubine, one must be professional.

Actually, the profession of an imperial concubine is pretty good. The emperor will accompany you in eating and drinking, and even pay you for it. What’s not good about that?

- Description from Novelupdates

Beta: Ahhh! Damn it... When will the good day come?

Author: Well, don't ask me, I just got here.

Beta: Fuck it! I want a good story.

Author: Junior, trust this senior, this is a good one

Beta: Arggh! Shut up! I hate it.

Author: courting death! Go and ask Yama how good this is.

Beta: Y-You, how dare you?

Author: I will give you 10 breaths of time, cripple your cultivation, and scram!!

Beta: Good! Very Good!

Author: *Raises his eyebrows and turns beta into useless dust particles*

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Chad: senior, I have been enlightened, I wish to know more about what you have in this ancient script.

Author: ah! An intelligent and wise junior, you have raised a very good question. Here are things this forbidden ancient script contains.

•Sinful activity: this book contains the profound sinful activity of balancing the Yin and Yang, by, shoving the mighty Yang rod in the Yin Hole.

•System - MC relationship: fuck... Ahem* Ahem* sorry for tongue slip. Forget the classic old system, here take this hot waifu tsundere system. ( not that edgy )

•Steal everything: junior! Are you tired of Mc only stealing the jade beauties that were created for the protagonist? Well, let's process further and add the Protagonist's mother, aunt, and sister, into Mc's harem.

Chad: oh! The senior really blessed me with such a divine forbidden Scripture, here take my money and give me the chapters.

Author: oh! Ho Ho! I haven't finished yet.

Here are a few more.

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!