"This is a world built upon Concepts."

Half of humanity possesses a mysterious energy known as Aura, granting them strength far beyond ordinary people. Among them, only a rare few awaken an even greater power—Concepts.

Those known as Concept Wielders can reshape reality itself. By channeling Aura through their Concepts, they twist the world according to their own nature. The strongest among them are capable of unleashing Concept Release, the ultimate manifestation of their power.

But humanity is not the only race blessed—or cursed—with Concepts.

Beyond the walls of civilization lurk the Concept Demons, monstrous beings driven solely by their Concepts and an instinct to hunt mankind. Forced into seven fortified cities, humanity survives only because the Combat Corps stand between them and extinction.

Among those seven cities, one shines brighter than all the rest.

Led by the legendary Hero Tia, Helios is celebrated as the safest city in the world.

Yet its peace rests upon a single, fragile lie.

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Ethel is a Lost One, a Concept Wielder whose Concept—Heart—allows him to perceive every incoming attack before it lands. Once, he dreamed of joining the Combat Corps. A tragedy buried that dream long ago.

But when fate exposes his hidden power during an unexpected encounter with a Concept Demon, he finds himself recruited by Hero Tia herself.

Drawn to her unwavering determination to protect everyone, Ethel chooses to fight once more.

Yet the closer he stands beside the city's greatest hero...

...the more he realizes that the one carrying Helios on her shoulders is also the one closest to breaking.

She has saved countless lives.

Except her own.

As the burden of protecting an entire city slowly consumes its brightest sun, Ethel must fight not only against the Concept Demons threatening humanity, but also against the invisible despair eating away at the hero everyone believes to be invincible.

Because when the sun of Helios finally burns out...

Dawn will never come again.