Yamada Yuuki is an ordinary college student with an extraordinary hobby: the classical martial art of Kukishin-ryu. Until one fateful day when a demon rips through the fabric of space-time, abducts everyone in his dojo, and transports them to another world. To return home, Yamada and his friends must join forces with other displaced humans to conquer the dungeon that runs through the heart of the world. Standing in their way are endless hordes of bloodthirsty monsters and countless traps. Armed only with steel, faith and guts, they must battle their way through the winding catacombs to confront the demon waiting at the bottom floor. Yamada was once a student. Now he must become a samurai.