[Baka-Updates] In this world, humanity has been driven underground to live like moles, hiding from the fearsome monsters which roam the surface. The monsters are impervious to every sort of weapon known to man. The only ones with the power to defeat them are the Ayanashi. One day, in one such underground city, a pair of siblings encounter a mysterious boy covered in wounds. The boy introduces himself as Holo, and in the following days slowly opens up to the pair…until a monster from the surface descends upon the city, laying waste to everything in its path. Holo stands to face the threat, brandishing a flaming short sword attached to his right arm. And so, the story of bringing light back to a world of everlasting darkness begins.
Humanity now lives underground. The surface of the world is pitch black, and taken over by deadly monsters. The only people brave enough to venture to the surface to fight these monsters are the Ayanashi. In this story we meet Horo, an Ayanashi out for vengeance against the person who killed his brother. Horo has always hated being around other people, but how will he cope now that he is all alone...?
