It will be the third StarCraft II product and will be released separately from the other two games, Wings of Liberty and Heart of the Swarm, occurring after them chronologically, beginning immediately after the ending of Heart of the Swarm. It is expected to be priced as an expansion.
By 2013 Blizzard had begun working on Legacy's story, scripts and missions.
The protoss were being systematically exterminated and were dying out from sheer age even before the Great War. The protoss have been picked off one-by-one, and their shattered civilization will fracture as something even worse happens, forcing a leader to save them from annihilation.
The protoss will be at the forefront of the story. Jim Raynor and Sarah Kerrigan will feature in the story, but Amon is the primary issue. Chris Metzen has likened the story to that of the film 300, with a small force engaging a much more powerful one in a desperate last stand. The storyline will conclude the StarCraft II trilogy.
The campaign will focus on Zeratul as its main character.
The protoss campaign will be based on diplomacy as the protoss factions splinter. The player will work with different protoss tribes and sects, helping leaders of some sects which will anger others. Using units from one side may preclude using units from the other side and alienating one or another sect may cut the player off from part of the campaign. The ultimate goal of the campaign is to unite the various tribes into a viable, unified force that can ensure the protoss' survival.
It has been indicated that Nova will make an appearance in the game.
Chris Sigaty has expressed doubt that new units will be added to the game, and that if they are added, it is likely that other units will be removed from multiplayer.
↑"The Protoss are sort of a troubled species. They're being systematically exterminated, and were being exterminated long before the Zerg arrived. They were starting to die out from their sheer age, but now that the Zerg came and their home world is gone, these guys are really having a lot of trouble." Dustin Browder, Jonathan Ross. 2009-06-29. Destructoid interview: StarCraft II's Dustin Browder. Destructoid. Accessed on 2009-07-23
↑"What we're talking about for the Protoss campaign is -- y'know, the Protoss are a shattered civilization, right. They've been beaten and pummeled by the brutality of the StarCraft universe for years and years and years now, and we might bring into the campaign something even worse happens to them, and they ultimately just fracture into all these different factions. And so you are working as one of the Protoss Heroes trying to re-unite the Protoss before annihilation." Dustin Browder et al. 2009-09-04. BlizzCon 2009 StarCraft 2 Fansite Q&A - Part 4/5. Youtube. Accessed 2009-10-07.