Arifureta Shokugyou de Sekai Saikyou (WN) - Chapter 474

MC (female protagonist) dies in a plane crash and wakes up in the body of a beautiful but corrupt and lascivious prime minister in ancient times, Zhang Qinglian. As circumstances decree, he (she) cannot reveal that the original owner’s soul is gone else calamity might occur. So he (she) decides to walk a righteous path, determined to help the lovely but simple little emperor rule the country. Not backing down after facing torture, not losing courage, destroying rebellions and facing off with scheming princes.

- Description from Novelupdates

Have you ever thought that the state of the world as it presently is, could revert to the laws of the ancients? When a series of strange incidents beginning with the disappearance of his friend led Luo Yuan to question the possibility of an apocalypse, he becomes embroiled in the midst of a global-scale chaos.

Arren was reincarnated as an extra in the book world. However, unlike the others, Arren was determined to play his role well and be the best extra ever.He was successful until that one unfortunate night that would make his second life an unpredictable one. He also began to doubt that perhaps... He wasn't the useless extra he always thought he was.R18.OMEGAVERSE/ BL

I finally managed to kill the demon lord.