Sekai ni Hitotsu dake no R

In a world consumed by chaos and darkness, a warrior named Urus is left shattered after demons slaughter his entire family. Driven to the brink of madness by grief and an unyielding thirst for revenge, he learns of Kelg's Pub—a renowned gathering place where heroes reincarnated into this realm seek companions to aid them in their quest to defeat the Demon King. Desperate for purpose and hoping to be chosen by one of these legendary figures, Urus journeys to the tavern, unaware that his arrival will set him on a far more harrowing path. Instead of joining a hero's party, Urus is subjected to a bizarre summoning ritual that brands him with the weakest possible class and marks him with a mysterious letter "R." This unexpected outcome plunges him directly into the true, hidden darkness of the world. Stripped of conventional strength yet burdened with an enigmatic mark, Urus must now confront terrifying mysteries that defy everything he thought he knew. What does the letter "R" truly signify? What is the sinister nature of the ritual that cursed him? And what unimaginable horrors lie at the heart of this broken world?