Honestly love how much the plot thickens. If there was one thing that I always criticized about Splatoon, it was the major lack of characters. Not just in quantity, but in quality as well. The series has no real protagonist, just a mere avatar with nothing to his or her name. The rest of the characters were as flat as it gets. This is the first time we actually see characters developing though, and this is the material you can buld a massive Nintendo franchise with.
I do still wish they created an actual protagonist for the franchise though, or even better center other characters to be the protagonists.. "Agent 3" just doesn't cut it. If you think "who is the face of Splatoon?", you think of a random Inkling. It honestly would have been great if they promoted the Squid Sisters to be the new protagonists of the Splatoon series in the single player mode. In this case they could have easily implemented having to play as Marie to save / fight Callie rather than making a purely customizable no-name Inkling the protagonist once again.