To answer the question in the episode title – “this isn’t my fault, is it?” – yes, Kumoko, this one is most definitely your fault, both directly and indirectly. However, it’s not entirely your fault, as you also unwittingly played into the plans of a country that was just looking for a trigger to go to war.
Her part in it all started with her destruction of the fortress that she encountered when exiting the Labyrinth, back in episode 13. Admittedly, the humans did attack first in that one (although out of legitimate concern about a dangerous monster escaping rather than malice), but accidentally going over the top in wrecking a human fortress tends to have consequences, and now they are catching up with her. The Word of God religion was already inclined to go after Sariella over their Goddess religion, and presumably they pushed Ohts to create an incident to justify a war. What better way to do that then to send an incompetent ambassador who would cause some incident concerning the so-called Divine Beast? The Ohts leadership may or may not have intended the ambassador to be a sacrificial pawn, but he certainly gave Kumoko an excuse to kill him, and Kumoko, not knowing any better, bit. Things are looking bad for baby Sophia’s homeland, and Kumoko staying involved is certain to complicate things further.
The troops marching on that incident allows the series to parallel to events 15 years later, where a different set of massed troops is marching on the elf village. (Honestly, it took me a moment to realize that the series had shifted time frames, since it ran so smoothly together and Hugo is not instantly recognizable in that helmet.) However, instead of focusing on Shun and crew preparing, most of the rest of the episode gives us Oka’s backstory, and that fills in numerous big gaps. It provides the first indication that the student roster we have been seeing when Oka talks about the other reincarnates is actually a visualization of her unique skill, which allows her to track the status and a future prediction on all her former students. That’s how she was able to find everyone, and that’s what drove her to action and helped define her identity in this new world. It is also why she has been so dodgy about details, though whether she actually is incapable of revealing that information, or would lose the skill if she did, is unclear. (The fifth novel does not clarify this, either.) Clearly, though, Oka is in as difficult a position as any of the reincarnations, as she knows when several are supposed to die (Natsume in the upcoming battle, but Kanata, interestingly, from being “stripped of of skills”) and is desperate to prevent that. It makes her into a much more sympathetic character.
Less certain is where Potimas stands in all of this. What we have seen about him over the previous couple of episodes suggests that he is a calculating rather than benevolent type, so he likely has unrevealed reasons for deciding to devote resources to helping Oka. Based on anime content only, the best guess is that it has something to do with his long-standing conflict with Ariel and/or the Pontiff of the Word of God. Another interesting tidbit is Kumoko’s second encounter with Black, aka “Guli-Guli.” Black at that point seems to be on friendly terms with Ariel, which may be connected to why he’s one of her generals in the future timeline. He also does seem to care about the state of the world, which makes his participation in Ariel’s war effort later on seem even odder. This conversation is more verbose in anime version than in book version (Kumoko does not explain herself in the novel), but it does show that Kumoko is serious about preventing the world’s collapse, even if she does sometimes stray into moral gray areas with her glee over getting XP for killing humans. Also, Ariel is shown in a more prolonged battle with Dragons, which aligns better with what happened in the novel than the final scene from last episode alone did.
The final montage is also interesting. It confirms that grown-up Sophia seems to be referring to Shun-timeline Kumoko (aka White) as Master, who is using miniature versions of herself for apparent remote communication. It also shows Merazophis, the right-hand mand of Sophia’s father, more clearly in this timeline as working with Ariel, as well as the robed figure who used the chakram back in episode 14 and another sword-wielding figure practicing outside a church; I do not believe that the latter character has previous popped up in the anime. This scene is a combination of two different traveling scenes in the fourth novel, but the way it is handled here works for the anime version.
The next episode’s title – “So I’m Not In This One, Am I?” – leaves me curious about its exact meaning, since I’m not sure how the story could avoid Kumoko for a whole episode at this point. Clearly, though, big events are coming again.