Following a delay of a little over a week, So I'm a Spider, So What? finally released its 24th and last episode on Crunchyroll. When the show first started airing, it had confused some viewers with its double timeline, with the past known as "prolepsis" but things mostly make sense now, while paving the way for a potential Season 2. So, let's break down the ending:
So I'm a Spider, So What? Ending Explained: What Happened to the Human Party?
Shun is a character who got some backlash due to being a stereotypical young male hero destined to be great, without having all that many qualities to make him unique and memorable. In the finale, we see him in a vulnerable position, as he and his party are on the losing side against Sophia and Kyouya.
When Anna dies protecting Shun, he instantly brings her back to life. This, unfortunately, results in activating a <Taboo> which seriously messes him up. In the world of So I'm a Spider this is activated when a character commits a taboo act and reaching level 10 makes someone understand the System of the world fully, resulting in extreme guilt and sickness.
At this point, a girl appears, whom the characters recognize as Hiiro Wakaba, one of the classmates, who is revealed to be no other than Kumoko, bringing the two timelines together.
So I'm a Spider, So What? Ending Explained: What About Kumoko?
The title of Episode 24 is "So I'm Still a Spider, So What? But this isn't strictly true. Sure, Kumoko is still a spider monster, in a sense, but she has an absolutely gorgeous human/spider hybrid appearance now, after having hatched from within an egg she laid beforehand, essentially recreating herself. She was able to achieve that due to a skill she got from her evil mother.
Over the episode, she and Potimas fight, until it's revealed that this is an android copy of him, rather than his true body. Demon-lord Ariel arrives and proposes a truce, which Kumoko accepts as Ariel destroyed the android and promises to give the real Potimas the same treatment.
The pair is joined by Sophia and Merazophis, and together they prepare to raid the Elf stronghold to subdue Potimas. They seem to genuinely believe that they are going to be the true heroes of their world… but will they?
A second season would provide some answers to that. Given the production issues faced during the current season, which peaked with the delay of the finale more than a week ago, it would be reasonable to expect a year or more to pass before any content comes up. Meanwhile, why not check out the ongoing manga or light novel of the isekai series?