Elf Tensei Kara no Cheat Kenkoku-ki - Chapter 7Book 2: -1: The Result of Effort

After being set up and killed by her half-sister whom her ex-boyfriend had cheated with, Mu Siyin woke up one day to discover that not only was she alive, but she had traveled back in time to 2 years before her death.

Octavius, misled by friends, embarks on a quest to clear his father's name, ultimately facing a tragic end with his sister.Their journey results in devastating loss, leaving him powerless and yearning for revenge against those who harmed his family. Spirits offer him a chance to reincarnate, but he refuses, saying;“What’s the point of a new life if I keep running from my problems”The entities are taken aback by his unwavering decision, having never encountered a spirit who refuses to escape their troubled past. They warn him about the evil being that now resides in his old body, but that only motivates him. He believed In the saying - to defeat a monster, you have to be twice as monstrous.Embracing his fate as The Phantom's Gambit, they traverse the shadowy path of retribution, their identities blur, secrets unravel, and the line between savior and monster fades.This is a tale of darkness and redemption, where justice is a blade, and revenge is the only way forward.

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

In the vampire-ruled kingdom of Mildelar, the Blood Games stand as the ultimate form of entertainment—savage battles between familiars, humans bound to their vampire masters through blood pacts. Far more than mere spectacles, these brutal fights determine the prestige of noble families, shaping their power and influence across the realm. Lyon, a young human saved from death by a blood pact with the alluring Arya Valakys—one of the king’s daughters—is unwillingly thrust into this cruel world. Bound to his mistress, he is forced into relentless battles to elevate her standing.Lyon, however, stands apart from other familiars. While they derive their strength from the fear of punishment, he draws his... from having dirty thoughts about his mistress!