College student Iwatani Naofumi is reading a book titled "The Records of the Four Cardinal Weapons" in the library when he is suddenly summoned to another world and told he has to save the world as the Shield Hero, one of the Four Cardinal Heroes. And one morning, he finds all his money and equipment gone.

Naofumi has obtained a whole load of abilities and skills, and his teamwork with Raphtalia is reaching perfection, too. To prepare for the incoming Wave, he upgrades their equipment and heads to the dragon hourglass to find out exactly when it will arrive. But there, he runs into Motoyasu and the other heroes once again.

After hearing of a village in the East that's being ravaged by an epidemic, Naofumi and his party head there to deliver medicine. The epidemic was caused by the corpse of a dragon that had been killed a month before and left there to rot. Naofumi's party accepts a job request to clean the corpse and head to the mountains where it lies.

Naofumi faces another Wave, this time in a remote village. With the help of the soldiers who volunteered to join him, he's able to secure the safety of the villagers, but the Wave shows no signs of letting up. He heads to fight with the other heroes, only to find a giant ghost ship floating in the sky.

Naofumi and gang stay on the attack despite being trapped in the Pope's Great Cathedral, but its sacred subspace nullifies his Curse Shield, leaving them one step short. Naofumi turns to another, newly unlocked Curse Shield, but the dragon's wrath threatens to swallow his mind whole.

After Naofumi survives thanks to Mirelia's help, she comes to visit him and tells him the truth behind the summoning of the heroes and the discrimination against the Shield Hero. She also promises to clear his name, and holds a trial for Aultcray and Myne's crimes.

It turns out that Glass, like L'arc, is also a hero from other world. Naofumi barely fights off their combo attacks and then corners Glass in a one-on-one battle, but is then faced with an all-important question: does he truly wish to protect this world?