The war for the dungeon reaches its climax! A hero has fallen. The threat of famine looms over humanity. The endless hordes of monsters inhabiting the world have grown even more powerful. The human military is at the breaking point. All hopes rest on the shoulders of Yamada Yuuki, a college student turned battle-hardened samurai. Armed with faith and steel, experimental weapons and new tactics, he must lead the way into the depths of the dungeon through swarms of horrific abominations and countless traps. But the dungeon itself is changing. And at the bottom floor, the demon ruler of the world awaits. The final campaign begins. A desperate, gruelling crusade to win through the dungeon and find a way home. Now is the time for Seisen. Now is the time for holy war.