Death March kara Hajimaru Isekai Kyusoukyoku (WN) - Book 16 - 16-61. Sage's Tower (9)

I am the sword.

Killing a man amidst a thousand miles, no one dares take ten steps.
Killing a man amidst a thousand miles, no one can take ten steps.
Killing a man amidst a thousand miles, ten steps? Not possible!

I am the sword, the sword is me,
On the path towards heaven, each shall wield their own.

- Description from Novelupdates

Everyone must have a few regrets in their lives, and for Mykel regret was publishing this novel on the internet. Because of this failed novel he wrote, made his career down the hill as an author. Thanks to this novel, he lost his passion and he lost everything that he had.

"I wish I can destroy this novel so that nobody will be able to see it or remember it anymore," Mykel said.

That was what he wished for, and for some reason, he went inside that novel of his and as himself in the story that didn't suppose to exist?

Mykel smirked and grinned as he looked at the system.

[You are the creator of this world, you will have the access to the command system. You are free to do anything as long as it is listed in the command system]
[Please enjoy and have fun]

"Heh, then I will turn this world upside down," Mykel said as he glared at the notification in front of him.

The hero who was killed by the demon king ended up reincarnated as the son of the one who killed him! Thus began the life of the hero who donned in the mask of the ideal demon prince to topple his own kingdom while doing his best to prevent anyone from discovering his identity―― But to do that and blend into the demon tribe society, he had to kill his former comrades. Nevertheless, to become stronger, to save humanity, he had to walk through all kinds of paths of carnage! This is the tale of the demon race’s fake prince destroying his own kingdom.

O Hero, Trample Those Who You Should Protect!

TN: Most part of the other character in the novel is depicted from a non-human perspective so expect something that is completely different from the common sense of human.

It was a life without regret. My parents were in good health, and I wasn’t homey enough for me to combine my studies and part-time jobs.