The Substitute Bride - Chapter 2066

Childhood sweethearts.
The most popular person in school is my childhood sweetheart.

- Description from Novelupdates

In the not-so-distant future, a group of Earthlings find themselves mysteriously transported to the Nexus Realm, a fantastical world besieged by monstrous creatures.With no way out of the craziness, they reluctantly joined forces with the realm's inhabitants to combat the constant threat of these otherworldly beasts.To defend the Nexus or Nexaria, powers were bestowed upon them with the promise of returning home after successfully repelling the monsters dangling before them like a carrot.Years passed, and the initial camaraderie between the heroes slowly began to crumble. Still, the Protagonist, Adrian Fenrir, with his power known as Analysis, played a crucial role in understanding the monsters' patterns and weaknesses. However, as the group became more adept at handling the threats, they grew increasingly independent and, perhaps, arrogant.One day, due to a series of mishaps, Adrian found himself surrounded by assassins. He tried his best to drive them off but failed and met a bitter end. It didn't take long for the assassins to do their work, and as per the contractor's request, they decided to dispose of Adrian's corpse by selling it to a mad scientist known for his experiments with creatures from the Nexaria.In need of a fresh subject for his latest project, the scientist transformed Adrian into a chimaera, a fusion of humans and monsters to be sold as a weapon for war.However, the scientist's plan backfired when Adrian, against all odds, regained consciousness within his chimaera body. Fueled by rage and the memories of his betrayal, Adrian seized control over his new body. Now reborn as a chimaera with the ability to absorb organs and gain the powers of other creatures, Adrian vows vengeance upon the mysterious contractor who sent the assassins for him.Once a battleground against monsters, the Nexaria now witnessed a different kind of conflict—one driven by betrayal, revenge, and the extraordinary powers of a vengeful chimaera.

In a Fantasy world in which a young girl with the Divine Protection of the Hero battles against the Demon Lord. In that world, Red, the elder brother of that young girl Hero, possessing the Divine Protection of the Guide which only grants a high initial level, fought in the initial party of the Hero.