Naruto: Uchiha's Unserious Saga - Chapter 187: The Art of Survival

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.

The dark underground dungeon was filled with countless ancient relics and treasures. Eerie, deformed, cursed objects... The abyss, catacombs, Ancient Gods, mythical races... Mechanics, cursed seal implants, and the gargantuan black towers... A peculiar mix of Alchemy, a drop of steampunk, two spoons of supernatural mystery, blending into a vibrant and colorful fantasy world. I am a puppeteer Alchemist. All that my eyes behold, becomes my puppet. Alone, I am an army!

The leader of the thousand demons, the Demon God Chun YeoWoon. Due to an unfortunate accident, he had been sent to the distant future.