Band Together! Quartet

'''Band Together! Quartet' (団結！かるてっと, Danketsu! Karutetto) is the twelfth and final episode of the first season of Isekai Quartet'' and twelfth episode of the full series overall. It aired on June 25, 2019.

Summary
The mobile fortress "Destroyer" has joined the last game! It's up to the quartet to grab its headband and win the game.

Plot
Class 1 and Class 2 now face off not just the teachers but also the Destroyer. Faced with the mobile fortress, Subaru suggests ignoring the Destroyer, but Ainz states that's not an option as the Destroyer is revealed to be wearing a purple headband around its head. Then, Roswaal attacks the team with his powers while Vanir and Pandora's Actor sends in their minions. As the Destroyer attacks Class 2, Reinhard uses his [Divine Protection] to shield his team. Kazuma believes victory to be hopeless and suggests giving up, but Tanya points out that nothing good will come if they give up and Kazuma gets remotivated a little. Then, Kazuma gets the idea of using his [Steal] ability to get the headband but finds that his skill will not work. Julius then invites Class 2 to participate in a plan, which involves dumping the responsibility to fight the Destroyer on Subaru and his team whilst Class 1 handles the teachers.

Subaru asks if Ainz could summon a horde of undead, and Ainz confirms it as Class 2 is nearly barreled over by the Destroyer. Tanya manages to barely raise a magic shield. They are saved thanks to Ainz, who buffs her shield with his own magic. Thinking that Subaru is planning something, Ainz throws his team in the air and summons an undead army, leaving the victory in Subaru's hands. However, it turns out Subaru has no plan, only asking in curiosity, though Tanya, flying with her two companions, decides to use a decapitation strike. Kazuma states that they will be hit by its beam. Subaru then decides to sacrifice himself, believing he will come back. Letting go of Tanya, he falls into a free fall and expects to be revived only to find that his ability is not working. To make things worse, the undead Ainz summoned are piling up to catch him, topped with fire from the Destroyer that is now targeting him. Luckily, Subaru is saved by Ainz before he falls to the ground. The Destroyer turning its attention to Tanya and Kazuma launches projectiles at them. Kazuma counters by using his slingshot to destroy each of the projectiles. Kazuma having served his purpose is pushed to the ground by Tanya who dives to grab the headband from the machine. Ainz rescues Kazuma, while Tanya engages the Destroyer. Kazuma using his 'luck' disables its legs allowing Tanya to capture the headband. Likewise, Class 1 succeeds in defeating Roswaal and the teachers. However the next day they are still in class. The class is disappointed that they were not returned to their worlds when they won the trial. Roswaal defends himself stating that he said "maybe" they could return to their worlds. Roswaal then calls to their attention to greet some new transfer students.

Trivia

 * This is the only episode in the Isekai Quartet series that lacks an opening song.