Pretty nuts episode.

Timeline wise, it means Kumoko and the rest of the class were born around the same time, 15 years prior to the current school timeline. No idea what it means for their teacher or the demon chick that recruited the asshole guy.
It also means that Fei is the youngest or even the last student to be reincarnated.

With Julius dying, that also means the demon lord perspective is the same time as the magic/hero school. Only Kumoko's is super early, since Fei was that egg, and the spider silk scarf was made from Kumoko's silk. Also shows us that while Kumoko is expressive and cute from her perspective, she's very spider-looking from human perspectives.

The meat of the reveals is probably D and the other administrator guy. He's sitting on the Demon Lord's council now. His discussion with the demon lord feels strongly like a red herring to me, about how they met all these years ago and who ever could have imagined their relationship would work out the way it does.

So...D doesn't own this world, but she's acting as an evil deity to this world, fucking with it for her own entertainment. The other guy specifically got tipped off when the dragon died, but not anything else Kumoko has killed so far. So he's associated with dragons? Therefore Fei? But he's working with the Demon Lord in present day?! So many more questions than answers!

And he knew that Kumoko had something to do with D. He couldn't translate for Kumoko, but D could. Should we take that to mean the reason they all reincarnated here specifically is D?

If she's an evil god, then that might explain why their teacher feels cursed or bound to not actually tell the other students what's up, but she does know where they are. That seems right in line with D's sickly sweet voice, plotting horrendous evil and cruelty for shits and giggles.