Sequel to Dragon Quest Builders. The story takes place following the events of Dragon Quest II, it expands upon the original story of DQ2 and elaborates on the nature of the game's villains: Hargon and his cult as they control an archipelago, actually a very elaborate illusion as well as Sidoh (Malroth), God of Destruction who happened to be reincarnated as your sidekick.
This tag implicates dragon_quest (learn more).