Episode 10 of "Nanatsu no Maken ga Shihai Suru (Reign of the Seven Spellblades)" is a whirlwind of intense battles and emotional confrontations. The episode begins with Oliver and Nanao training early in the morning. Oliver emphasizes the importance of mastering spellcraft before combining it with swordplay. Their training is interrupted by Katie, who introduces them to Marco, a troll she has befriended. Marco is brought into the labyrinth by Miligan, who reveals that he gifted Katie the workshop as an investment in her future potential.

The group, now including Marco, ventures deeper into the labyrinth. They are confronted by Ms. Cornwallis, Stacey, and Fay, who challenge them to a duel for their medals. Joseph Albright, a first-year student from a prestigious family, joins the fight, turning it into a three-on-three battle. The duel takes place on the second level of the labyrinth, known as the lively forest.

The battle begins with Oliver facing Joseph, while Nanao and Chela take on Ms. Cornwallis and Stacey. Oliver and Joseph engage in a fierce swordfight, with Joseph initially dismissing Oliver's techniques as textbook maneuvers. However, Oliver lands a hit, proving his worth. On the other side, Nanao and Chela fight their opponents. Stacey reveals her complicated relationship with her half-sister Chela and her desire to surpass Michela, her uncle's true daughter.

The duel takes a shocking turn when Fay transforms into a werewolf, a painful process for him. Despite the agony, Fay continues to fight, demonstrating his loyalty to Stacey. Chela and Nanao acknowledge their opponents' resolve and vow to fight with their full strength.

The episode leaves viewers on the edge of their seats, wondering how this battle will conclude.