While reading a book on weaponry, college student Iwatani Naofumi is transported into another world where he must take up the mantle of the fabled Shield Hero.

Unable to use a sword, Naofumi searches for a partner, but he can only afford a sickly demi-human slave, whom he tries to train in a harsh manner.

Naofumi has obtained many abilities and skills, and his teamwork with Raphtalia is improving as well. To prepare for the incoming Wave, he upgrades their equipment and heads to the dragon hourglass to find out exactly when it will arrive.

Upon learning Naofumi employs a slave, Motoyasu angrily challenges him to a duel and the king ups the stakes when he threatens to take Raphtalia away from Naofumi if he loses.

While seeking to reapply Raphtalia's slave crest, Naofumi purchases a monster egg that soon hatches to reveal Filo, the newest part of his team.

Filo shows her ability to take human form, but requires special clothes. Naofumi and his party search for a gemstone needed to make her clothes, and help an imperiled trader along the way.