The One Who Shines in the Darkness

In a distant future, the Garo armour has lost its golden shine, and its power as a consequence. The new holder of the Garo title—Ryuga Dogai—is summoned to the metropolis of Volcity and tasked with eliminating the Madou Horrors, a rare breed of Horror, who have infested it. Who are the Madou Horrors, and what is their connection to the lost shine of the Garo armour?