In the Avalon Kingdom, there's nobody who didn't know about the monsters from Ein forest. But nobody knew exactly where they come from. Theories and rumors only circulate without any truth has been proven. But there's one thing that certainly needs to be done. Repel them. 100 year has passed since the first monster's appearance. They showed up every once in ten years, destroying everything in their sight.  The House of Conrad is chosen as the one in charge of taking countermeasures to the monster's appearance. Archibald Conrad, the head of the House who was also the Duke of the kingdom, inherit the authority from his predecessor to make policy regarding preventing the monsters from running amok around the kingdom. With his sons in the frontline, they are doing their best. But they sensed there was far more complicated and sinister happening behind the scenes.