Episode 10 is nowhere near as packed as episode 9 was, but it still introduces a handful of characters who will have at least some significance in future plot developments, follows up on the big ending plot twist of last episode, shows Kumoko's first real face-to-face encounter with humans, and ends on another potential major plot twist. Thus it has no shortage of things to talk about.
The fallout from last episode's ending starts off this episode. Schlain has mentioned before that he is only the fourth prince of his kingdom, but the scene where Schlain speaks to his father about becoming the Hero (and what that means) is, I believe, the first time in the anime where his other elder (half) brothers come into play. Of the two, Leston is the far more sympathetic one towards Schlain, while Cylis seems colder and more formal. That also makes Cylis' thoughts about this situation hard to read; his glances towards Leston and Schlain give a vague impression of being discontent with Schlain being the Hero, though why is not even hinted at. We just don't know enough about Cylis at this point to make any judgment calls here. What is certain is that Schlain, by staying home to prepare to be the Hero rather than continuing at the Academy, is going to be isolated from his sister and comrades, and that cannot be a good thing for his mental health right now.
The third important introduction is the wizard Ronandt. He is a big deal in the setting because he is the most powerful human mage, but he is important to the story at this point for two other reasons: he is the only named human character introduced so far in the human side timeline who has made direct contact with Kumoko, and that contact provides a sense of scale on just how powerful Kumoko is getting to be. There might be monsters in the Labyrinth who can still push her to her limit, but even the most powerful human wizard is in awe of her, to the point that the encounter gives him a heavy dose of humility. That he has had 15 years to develop his magic since then and still thinks that way shows just how impressive he found the “Nightmare of the Labyrinth” (i.e., Kumoko) to be.
Speaking of which, the utterly contrasting perspectives on Kumoko sure were interesting, weren't they? Viewers have always seen her as a cute spider, but humans perceive her as a horrifying monster despite her failed efforts to communicate. She also either did not restrain herself or overestimated how tough they were (perhaps the latter, since humans did drive her off before), leaving her trying to convince herself that slaughtering human troops was morally justified. While it is a little hard to argue that she acted in pure self-defense – since the human troops just went on the defensive against her and she technically made the first offensive move – she also has been living for months now in a “survival of the fittest” environment and has had two bad encounters with humans before, including one where they actively try to pursue and kill her. Because of that, the morality of her actions could be seen as irrelevant, though it still makes for an interesting grey area. Our little spider might be edging towards being a true monster beyond just her race.
The appearance of a Queen Taratect (presumably what the mother spider was) at the destruction of the human fort where Julius died raises questions which cannot be answered right now, but certainly reinforces the spider connection for the Demon Lord. The more immediately involving twist is the note that the episode ends on, with Kumoko unwittingly raising Taboo to Level 10. The “installing information” pronouncement that follows Kumoko's achievement sounds ominous; what will Kumoko learn as a result? And if there is knowledge so important that it is hidden behind this label, why allow any path within this system to it? Perhaps we will find out next episode.
Finally, in adaptation terms, this episode jumps all around in the third novel, with the scene involving Schlain and his family being near the beginning and the scene involving the Nightmare of the Labyrinth being near the end. The adaptation is skipping one significant spider-side scene and recontextualizing when certain things happen, but none of the changes have a significant overall impact on the story and they continue to align what's going on more smoothly. The first few volumes of this series are maybe the least linear of all isekai stories that I have read, but it is being handled about as well as I could have hoped for.