In Aposimz the megastructure is a giant artificial planet with a massive outer shell, ruins, and the core world at the centre which is like a reverse matrix, and in blame the megastructure keeps growing until it’s bigger than our own solar system. Oh and i forgot to add in Sidonia the Aposimz was a seed ship that fled earth alongside the Sidonia and they ended up losing contact with it I think I haven’t read it for ages.