Naruto System in One Piece - Chapter 26: Flying Thunder God Slash

…but it seems pretty doable.

Lucas Carter, a stressed-out office worker, never expected to die, let alone be reincarnated into a brutal world where beasts are the key to power. Born as the heir to a lowly barony, surrounded by elves, beastkin, dragons, and demonic clans, he was supposed to be a mere pawn, nothing more than a stepping stone for the true power players.But fate had other plans. Armed with a modern strategist’s mind and a mysterious system that grants him the ability to tame legendary beasts, Lucas quickly rises above the limitations of his birth. With the power to summon beasts, fuse them into deadly weapons, and unlock hidden skills, Lucas is no longer just surviving—he’s thriving.By his side are his loyal companions:Umbra, a Black Nemean Lion with indestructible fur and devastating roars that disrupt magic.Zephyra, a playful yet fierce Baby Wind Dragon who wields the power of wind itself.With his growing army of legendary beasts and his tactical genius, Lucas begins to build an empire. Along the way, he forms bonds with powerful women from every race, all while navigating the dangers of political intrigue, betrayal, and the constant threat of rivals who want to take everything he’s earned.One beast at a time, Lucas will carve his name into history. But in a world where strength is everything, can his cunning and loyalty to his beasts truly make him the ultimate ruler?

Betrayed by his sister. Betrayed by chosen one's humanity. Betrayed by the Gods.That was how the life of Leonard, the Defier of Fate and the world’s greatest heretic, came to an end.When demons invaded human lands, he received a revelation from the Goddess. She commanded him to act as a spy, to infiltrate the enemy ranks and expose their secrets for humanity’s sake.To fulfill this mission, he had to sacrifice a part of his soul. He accepted a demonic contract, surrendered his soul, and became a demonic human. Risking everything, he provided critical information to the humans and helped them turn the tide of battle.But then, he had a shocking discovery.The war was nothing but a gambit between various gods and before he could act, the war was stopped out of nowhere.In an unexpected turn, humans and demons put aside their hatred and signed a peace treaty.Before Leonard could make sense of it, he was betrayed. Both demons and humans joined hands to kill him.“Fuck! If there is a next life, I swear I will tear you gods apart!”With this scream, he thought his suffering was finally over.But…When he opened his eyes again, he found himself in the body of Kael Veydrin, the son of the Grand Duke of the Heizen Empire. But this new life was no different from the last.His sister wanted to get rid of him.Born with clogged vessels and no talent, he was nothing but a disappointment.A subject of fun and ridicule among the fellow nobles.Despite rebirth, nothing seems to change.The cursed fate.The distorted history smearing his name.A world that was against him.Leonard, now assuming the identity of Kael, let out a low chuckle.“Don’t worry, Kael. I will have revenge for both of us.”“They called me heretic right? I will show them how a true fucking heretic acts.”Follow Kael's journey, as he fights against the fates and injustices to drag the ones ruling above.

The simulation is over, and the entry is obtained: a showdown!

Looking at this entry, Zhao Meng was stunned.

“How should this term be used?”

“Hey! Here’s a wounded fox!”

…

A few years later, a woman who looked like a fairy appeared in front of him, and said:

“My lord, I’m here to repay my favor!”

This book is also called “Starting from Transforming Monsters”

- Description from novelbuddy