Join In! Rivals (参戦!らいばるたち Sansen! Rai baru-tachi) is the tenth episode of Isekai Quartet. It was first broadcasted on June 11, 2019.


Roswaal announces to Class 2 that Field Day is coming, eliciting confusion to Subaru, as the class already just had a field trip. Roswaal clarifies that it will be a competition that they will have to win. To add enticement, he informs that if they win the competition, the class may be able to return home. This remark catches the attention of the entire room. But Subaru interjects, asking who will they be competing against, as Class 2 is the only class group in the entire room. Roswaal reveals that Class 2 will be competing against Class 1, who are in the room next door. Subaru runs to the next room and, after looking through the window, discover that the next class is be filled with other characters from different worlds, some of whom are from his world.

Subaru is especially shocked to see Reinhard in the class. The teacher, Vanir, politely asks Subaru to refrain from disturbing his class. Roswaal, Tanya, and Ainz come over to see before the former reminds them to return to class. Ainz and Tanya know that there wasn't a class there before. Roswaal attributes it to how the world works.

After class, Tanya, Ainz, and Subaru discuss the people in Class 1. As Ainz has learned that the Pleiades are in Class 1, and Subaru's comrade, Reinhard, is there as well, Tanya deduces that other people from their worlds are trapped in the current world. Since Roswaal stated they can go home if they beat Class 1, Ainz suggests they should comply. Tanya asks about the strength of Class 1. Ainz is confident that the combat maids will be no issue. They ask Subaru to tell them more about Reinhard, only for him to state that the young man possesses Divine Protection, which is insanely powerful. They hear a commotion outside and see Aqua recognizing one of the students from Class 1, Chris. Kazuma and Darkness also greet Chris, with Chris warning them that if they die in this world, they can't be revived. Aqua demands to know why Eris isn't doing anything to stop this, only for Chris to state that she is not in control of the situation. Aqua finds it amusing that Chris has no idea what is going on, only for Darkness to be annoyed at Aqua for insulting her goddess, even making fun of Eris' fake breasts. While this is happening, Shalltear, who is shown hanging out with Rem and Albedo, suddenly sneezes. Rem asks her if she is feeling alright, while Albedo thinks it's because someone is talking about Shalltear's fake breasts, which angers Shalltear.

In the end, Aqua earns a blow on the head, causing her to break out in tears. Chris tells Kazuma and Darkness that they will be rivals now and to be careful as they cannot be revived in this world. Subaru, who is overhearing this, wonders if his [Return by Death] ability, which allows him to come back to a saved point in his life after he is killed, won't work. Subaru is hesitant to tell his new friends his ability but decides it's worth a shot. To test it out, he covers Tanya's ear and tries to explain his ability, only for him to stop when he feels death looming for his penalty. Realizing it is still in effect, he stops, only to be run down by Hamsuke and a Death Knight. Hamsuke and the Death Knight are then given a blow to their heads by Aura, who apologizes for what happened, revealing that they just got excited for some reason. When Ainz asks what made them do this, Subaru says that it was his doing, revealing that he has an ability that has a side effect of attracting magic beasts but had no idea that it also attracts the undead. When Ainz asks if it's some kind of curse, which Subaru confirms, Tanya realizes that both she and Subaru have problems with annoying curses, only for Subaru to point out that Hamsuke is chewing on his head again. Hamsuke and Death Knight are then sent back to their cage, with Hamsuke being forced to hold a sign saying "I am a Bad Hamster."

Class 2 gathers together to come up with a plan to win and return to their worlds. The only one to object is Kazuma, as he finds the current world better than his own world. However, Kazuma's friends berate him for his selfishness and remind him that he still needs to defeat the Demon Lord in his world. Kazuma rebukes that there is no way he could accomplish that and prefers to be lazy. The other classmates find this disagreeable and declare they have no intention of losing. However, Kazuma still refuses to help, prompting Tanya to offer him an 'initiative' to motivate him, which mostly involves forcing Kazuma to run for his life as Tanya and Puck bombard him from the air with magic, with Megumin also joining in.

Characters Introduced

In Order of Appearance


  • School

Play Notes

  • Written on the chalkboard in Class 1 is "Absent: Tweet Nika Teyanen." In Youjo Senki, Tweet Nika Teyanen is a soldier in Tanya's squadron who was discharged after eating a rotten potato.
  • Tanya has Kazuma run while carrying a shovel just as she does to her unit when training them.
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