Khemia takes place 2 years and a half after the end of Adastra. The story deals with Amicus going on Khemia to complete the Alliance with the Khemians. In this game, you don't play the Human though. You play a young wolf named "Scipio" (The one you see in the pay-off at the end of Adastra). Khemia's likely to give us a Neferu x Scipio relationship, while Amicus deals with the bureaucratic shit (poor baby wolf :c)
If you want even more, you can play Interea. Interea's a spin-off to Adastra. It takes place DURING Adastra when Amicus takes the Human on a trip around the Moon. (In Adastra, this even is summed up in a few sentences. There also will be a likely plot regarding Alexios. Since he isn't shown but simply mentioned in Khemia, I supposed they'll kill him in Interea? That's no spoilers, don't worry, just a simple guess).
NB: Both are still under HEAVYYYYY development. In fact, Khemia's gameplay duration is around 30/45min then you're hit with a "To be continued..." whereas Interea lasts 20min only. (You're then also hit with a "TBC" screen)
This is due to a HUGE writer block (lack of inspiration) from the writer (Khemia) and also because the writer just moved houses, quite the distance, and had to stop writing (both games).
Khemia's been on hold for many months now, and Interea hasn't received any huge updates in a while now. However, things should get back to normal soon. I guess.
NB2: (I'm so invested LMAO) We still don't have any info regarding a possible "Adastra 2". However, this very morning, HAPS (Chara Design for Adastra/Khemia/Interea) just dropped an Amicus drawing on Twitter saying "Preview". Is that a sign for things to finally move? Who knows ;P