Manga Ayanashi

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...?