Splatoon 2 is a multiplayer third-person shooter in which players control characters known as Inklings and use colored ink to attack opponents and clear goals. Inklings can alternate between humanoid form, during which they can fire ink with their weapons, and squid form, which allows them to swim through ink of their own color in order to move quickly and replenish ink supplies.

The Great Zapfish that powers the city has gone missing, as has Callie of the Squid Sisters. Fearing that the Octarians are once more involved, Marie assumes her role as Agent 2 of the Squidbeak Splatoon and recruits an Inkling from Inkopolis Square, the player character, to become Agent 4 and investigate.