Stormblood marks a shift in the ongoing conflict with the Garlean Empire. Players lead rebellions in the imperial provinces of Ala Mhigo, an Eorzean city-state conquered twenty years ago, and Doma, a Far Eastern nation with a proud ninja tradition. These regions are administered by the emperor's son, Zenos yae Galvus, whose brutal oppression of the conquered imperial subjects impels the player to act. Traveling these diverse lands, players join forces with the Ala Mhigan Resistance and the deposed Crown Prince of Doma. In addition to adding new areas, the expansion pack increases the level cap, adds two new character classes, revamps the battle system for existing combat classes, and introduces swimming gameplay.
Stormblood was well received upon release and earned nominations for "Expansion of the Year". In August 2017, Square Enix announced that the title had reached a cumulative total of 10 million accounts. As with its predecessors, major content patches were scheduled for every three months. The first one—"The Legend Returns"—was released on October 10, 2017 and premieres a storyline written by Yasumi Matsuno that features his signature Ivalice setting, as well as a special "Ultimate" difficulty battle, designed to be the most challenging content in the game.
The gameplay and quest structure of Stormblood largely match that of its base game. As with many MMORPGs, players interact with each other in a persistent world that responds to their actions. A dramatic revamp of the battle system accompanies the level cap increase to level 70. The changes fall into three broad categories. First, many underused or redundant abilities were combined in order to reduce the number of buttons needed to play each class effectively. Second, the cross-class system was replaced with a more general cross-role system that ensures that players have all the tools they need even with just one class leveled. Finally, all classes gained a "Job Gauge" that displays all class-relevant information in a more visible and engaging way. Two new job classes were introduced as well—the katana-wielding Samurai and the versatile Red Mage, both damage-dealing classes. These jobs begin at level 50 with their own storylines connected to the new settings. Unlike Heavensward, they are accessible to any player with a level 50 class, regardless of story progress.
In addition to new dungeons and raids, Stormblood introduces a new player versus player (PvP) mode called Rival Wings. Two teams of 24 players face off in goblin-run war games. Points are earned by destroying opposing bases and robot minions. Players are able to call down and pilot giant mecha after achieving certain objectives. The mode has been compared to multiplayer online battle arena (MOBA) games.
Finally, a new area called Eureka the Forbidden Land debuted with Patch 4.2. Its gameplay is inspired by "old school" MMORPGs, including Final Fantasy XI among others. In Eureka, players must use the Magia Board to exploit monsters' elemental weaknesses and increase their Elemental level. Unlike the rest of the game, players lose experience points if defeated and can even "Level Down". Later sections of Eureka permit the use of Logos Actions, which are unique spells and abilities that players craft using materials found in the zone. Eureka culminates in a high tier raid called the Baldesion Arsenal that requires 56 players to work together to overcome it.