Nintendo revealed quite a lot in the latest Nintendo Direct and one of those reveals was the first paid DLC making its way to Splatoon 2, the Octo Expansion.
This is the first paid DLC to come to Splatoon 2 and will allow for players to play as an Octoling for the very first time. From the above video we can see Agent 8, who awakes without her memories in a dark subway platform.
Players will have 80 missions available to play, as well as a special reward that once the DLC is complete and Agent 8 reaches the surface, will be the ability to play as an Octoling in multiplayer matches.
Here is what is said in the description of the Splatoon 2: Octo Expansion description: "The first paid DLC is coming to Splatoon 2 this summer. Play as an Octoling for the very first time in this large-scale downloadable content for the Splatoon 2 game! This full-on single-player adventure spans 80 missions starring Agent 8, a new character who awakens without her memories on a dark subway platform. Navigate this mysterious underground test facility in a desperate battle to reach the surface of Inkopolis. Escape from these twisted depths, and you'll finally be able to join multiplayer* matches as an Octoling!
You may think you know everything about the world of Splatoon, but these waters run deep, and so does the lore. Purchase this content today for immediate access to special octo-themed in-game gear."