This article is too short to fully cover its subject.
Theanos is a post-apocalyptic world, where everything was destroyed in a great conflict referred to only as 'The War'. Of the survivors of The War, some scientists made a large 'virtual world' complex, where people hook themselves up to a machine and live out happier lives in virtual fantasies, with the real world being as barren and unlivable-in as it is. It is the setting of Beast Signer.