is this VN before or after adastra I would like to know so I can go in order, please and thank you.
Adastra is the first game you should play of the three games available.
Interea is a side-story (some sort of spin-off) happening during Adastra (in the Adastra, what's happening in Interea is briefly summed up, in a few lines).
Once you played Adastra, you can either choose to play Interea, or Khemia, a sequel to Adastra happening 2.5 years after the events of the main game. Keep in mind however that Interea and Khemia are still under heavy development, therefore you'll face a "To Be Continued..." 20min after you started playing.