Ten years ago, the sky suddenly tore open and the Gates appeared.

In an era of despair where monsters poured out, superhumans known as 'Sentinels' emerged—individuals whose senses become overloaded to the point of madness—along with 'Guides,' the only painkillers capable of quieting that agony.

Hajin was originally a child who shared no blood with the family.

To provide a sturdy fence for Guest, who would eventually be left alone in the world, the parents brought home the most neat and quiet boy from the orphanage they had long supported. The foster parents gave their warmth unsparingly to Hajin, and Guest grew up loved in their embrace.

Even when the Gates opened ten years ago and the age of chaos began, that family endured peacefully by leaning on one another.

The tragedy struck five years ago, just as Guest reached adulthood.

During a family meal, a Gate suddenly burst open, and the parents lost their lives before their eyes. Amidst that bizarre despair and terror, Hajin awakened as an S-Class Sentinel, driven by the instinct to protect his sibling.

He was forcibly admitted to a national institution before he could even dry his tears, but no rules in the world could suppress Hajin, who had become an uncontrollable S-Class bomb.

As if mocking the Center's control, he often returned to their private home. While he might have been a grim reaper mercilessly slaughtering monsters outside, he never showed even a single drop of blood in front of Guest.

Returning in clean clothes with the scent of blood perfectly erased, Hajin would simply hold Guest's hand with a weary expression, still maintaining his position as a harmless and pitiable guardian.