Margrave's Bastard Son was The Emperor - Chapter 313

Waking up again in his seventh reincarnation, prince Jing Beiyuan found himself back in time, when everything had yet to be set in motion. Having been given a second chance, Beiyuan had to survive court and decide whether it was finally time for him to let go of his feelings; all while trying to handle the youthful, innocent force of nature who had suddenly barged into his already complicated life.

- Description from Novelupdates

This legend tells the tale of the protagonist, Kuroki summoned to protect the demon king from the hero.

Kuroki, unbeknownst to him, suddenly came to another world. He was summoned by the demon king, Modes. The territory which the demon king overrules was in the midst of being destroyed because of the hero. He had no choice but to bow before Kuroki.

“Please save us, Savior Dono!”

Kuroki nodded, deciding to save the demon king due to an unexpected turn of event.

Eren Idril died as an old, decrepit, and piss-poor adventurer by the maws of a D-Rank monster. He had a lot of unfulfilled dreams and desires that couldn't see the light of the day after the light in his own eyes died down.

But fortunately for him and unfortunately for the world, that wasn't his end. Eren was somehow dived back in time when he was a mere teen, attending Lionheart Academy for adventurers.

When life gives him a second chance, Eren decides to exploit it to its fullest. Experience his vile deeds as he partakes in them without feeling the slightest bit of hesitation.

Ethan was just an ordinary guy until he woke up in the world of his favorite novel, Gods’ Final Requiem.But this isn’t a story where the hero wins. It’s a tragedy where the protagonist falls, the world crumbles, and the Demi-Gods and Outer Gods consume everything.And now, Ethan is here weak, talentless, and completely insignificant. A nobody in a doomed world.Yet, when an Empire Academy Admission Letter lands in his hands bearing his name he realizes something is wrong.More than that, his status window hides two sealed abilities, something that never existed in the original story.This wasn’t supposed to happen.If the world is truly destined to fall… then maybe, just maybe, he can change it.But first, he has to survive