In the anime's opening, the main characters' relationships between each other has been perfectly established.
When we first see Tanya and Kazuma, the latter starts to tire out from running only for Tanya to kick him to get moving. It seems odd Tanya would be concerned or angry at Kazuma until one must remember how she died in her previous life: She(He) was killed by an employee that he fired for under performing and failing to prioritize. While Kazuma is the Only Sane Man, much of his traits are the exact match to that employee's. Tanya's actions were: A) setting Kazuma straight and B) making sure Kazuma doesn't pull any tricks on her.
Ainz and Subaru. Subaru has already died multiple times hence why he isn't bothered that he is literally speaking to death itself. Ainz would take a liking to Subaru since both want friends.
In episode 4, when comparing their experiences of being a Non-Action Guy summoned to another world, Subaru doesn't tell Kazuma about his frequent dying. In his home series, this is because he's been cursed by a witch, and if he tries to tell someone about it, that someone dies, so it's only naturally he'd leave that aspect out here as well.
Kazuma would likely hold it against Subaru too even if Subaru was able to tell him about it. Whenever Kazuma dies, he doesn’t get a reset of the last few days and his body remains in whatever state it was in until Aqua repairs it. Not to mention said curse is the result of another woman being in love with Subaru, even if said woman is an extremely insane Yandere(and also a witch).
Kazuma has died 4-6 times in light novels. However, all of his deaths are painless and only once has his death made his life harder; it's therefore hard to say dying has given him any mental trauma, orc encounter aside. Meanwhile, Subaru still gets his assed kicked, has broken bones, and loads of trauma even without counting his deaths. Respawning also does not always save him from mental heartache or loss. That said, Kazuma would most likely not care even if he knew.
It makes sense that Ainz was able to quickly realize that Tanya was from Japan. In his home series, he was trying to gain the attention of anyone from Japan that was trapped in the same world as he was. He therefore would, even subconsciously, still be looking for one of his compatriots.
In episode 9, when Tanya was stopped by Ainz and Subaru from attacking Aqua under the suspicion that she is Being X, Aqua points out that she has been telling everyone that she was a goddess since the moment they first arrived, much to Tanya's confusion. This most likely not only has to do with the fact that Aqua hardly acts like a goddess, but the only reason why Tanya went berserk in the first place was that Aqua mentioned that she took Kazuma from his world. This was the trigger, since Being X also dragged Tanya from her world as well.
Why is it that, in Episode 10, Chris just randomly happens to know that Kazuma won't be able to get revived in Isekai Quartet's world? Well, that's because Chris is an avatar of Eris — as shown in their home series, Aqua needs Eris's help to revive Kazuma by opening the gate back to the world on Eris's side of the fence. If Chris says Kazuma can't revive, it's probably because Eris is stuck in Isekai Quartet's world too, and she can't do anything about it.
At the start of season 2, Naofumi is wandering around trying to figure out what's going on, Raphtalia is running around trying to find Naofumi and Filo is just sitting in the animal shack. This actually makes a lot of sense because as the youngest and least mature of the Shield Hero trio her running around is liable to get her even more lost. When children are lost they are supposed to do one of two things, either seek an authority figure, like a police officer, or wait for their parent to find them. Since Filo can take care of herself, Naofumi probably told her to stay put in the event that they get separated and let himself or Raphtalia find her. Filo even tells the others who she is like a lost child is supposed to, giving them what they might need to find her parent. She wanders off with Aura and Subaru because, she's well, Filo.
During the dodgeball game we learn that, while she is always Subaru's ally, the one thing Rem won't stand for is mayonnaise, those familiar with the Re:Zero bonus chapters will recall Subaru seemingly liking the condiment so much that he is seen taking a bath in it. However we later learn from his mother that Subaru doesn't actually like mayo as much as he lets on. The truth is he partakes of because of how he and his parents bonded over their love of it. So why does Rem not stand with Subaru on team mayo? We are led to believe that it's because of the trauma of catching him in a bath of it, but as she insists, Rem is always Subaru's ally and there is only one thing she wants from him, for him to be honest with himself. Subaru choosing mayo is because of what his parents like, not what he likes, which is why she can't forgive it.
Pandora's Actor liking Viktoriya's German based uniform makes sense since Overlord's light novels reveal his outfit is based on the uniforms Neo Nazis' wore in a war twenty years before in Satoru Suzuki's original world.
When Filo talks to others she generally uses a nickname for them, particularly Ainz Ooal Gown, Lupusregina Beta and Beatrice. This is because she is less than 6 months old when she appears in the series and the Overlord cast tend to have long, hard-to-say names for someone of Filo's age, it's no wonder she uses Subaru's nickname for Beako and calls Lupusregina Wolf Lady, if she tried saying those names she'd likely bite her tongue.
Class 1 however, plays them straight, Reinhardt is potentially more powerful than Ainz, Julius being a very classical Chivalric Knight and Felt as a Secret Princess are fairly common trope. Chris is the only person in the Konosuba cast who is not led by her vices and the Pleiades generally play their role as the Quirky Mini Boss Squad very wellnote Better than the Floor Guardians really, as they never let their personality clashes interfere with their work. Finally the Shield Hero trio, while having some unique elements still include a classically powerful protagonist and side characters.
So far, there hasn't been anything truly violent happening within the series. However, it's implied that this could be the result of some outside force making sure that none of the characters harm one another. If that force didn't exist, could Aqua actually have killed Ainz or Ainz could have easily killed her. Or could Megumin's explosion spells have incinerated everybody?
Then there was Tanya's true thoughts about Viktoriya who felt that men didn't take any interest in her. Viktoriya was referring about the time at the war and Tanya dreaded that had things been worse, all the soldiers would have most likely gang raped the closest female they could find. Tanya felt actual relief that this hasn't happened yet.
The idea of Kyouhukou being in charge of detention is complete horror in itself. Episode 3 of Season 2 has him punish the detentionees by having cockroaches entering and exiting out of their mouths and ears and any other holes, the last part meaning their butt holes and lady parts.
The fact the PetelgeuseRomanee-Conti, Archbishop of Sloth is alive and hanging around. Suburu is going to freak out that his Archnemesis is here. Worse still it's implied he arrived independently of the other characters, meaning other Archbishops could show up.
Not just the Archbishops of the Witch's Cult, but any antagonist from any of light novel series in the crossover, even those that have been killed in their home series, can show up at any point. Which means a Legion of Doom, made up of sadistic killers, demon generals, Sociopathic Soldiers and so on, might appear in the future.
The implication that our protagonists hail from the same version of Japan becomes one when you remember how bleak Ainz's original world is, where corporations took full control of the world and pollution has extended to the point people need to wear gas masks just to go outside.
So...where does everybody go once the school day is over? We saw the Overlord group going somewhere once the day was over during Episode 2 , but it's unlikely that the Tomb of Nazarick was also teleported to the new world. Making this even more confusing, Episode 7 shows that Emilia is sleeping in an expensive-looking room that wouldn't be out of place in Roswaal's mansion where she lived in her home series, but where this room is located is left unanswered.
Well, we know that there are seemingly random houses placed on the streets of... this Small, Secluded World. Make of that what you will.
