It seems hell hath no fury like a Squid Sister scorned. Some recent story details about Splatoon 2 released by Nintendo hint the two soft-boned pop idols who captured everyone's hearts in the first game are at odds in the upcoming sequel for the Nintendo Switch.
If you visit Squid Sisters Stories, you'll receive insight from a seeming researcher who's recovered information on what happened to Callie and Marie after the last Splatfest battle. Though the girls were on friendly terms immediately after the "Callie vs Marie" Splatfest (from which Marie walked away the victor), their "unbreakable bond" looks to have dissolved.
If the event is being made note of on a site called "Squid Sisters Stories," it implies the sisters' falling-out involved more than a friendly handshake and parting of ways. At the very least, the band probably broke up. In the worst case scenario – well, I'm not saying I'd object to a single-player campaign that sees Marie lead a band of scrappy Inklings against a rage-twisted Callie.
As long as everyone has fun and nobody gets hurt for reals, of course.
The bad blood between Callie and Marie isn't a last-minute fabrication by Nintendo, either. If you look at the dialogue between the Squid Sisters before and after each Splatfest, you discover the half-hearted jabs become kind of mean over time. My personal favorite is Marie telling Callie "Science" only won over "Art" because "us scientists have actual jobs to do." Ha ha! She's got my number!
Oh, and Callie calls Marie a "grey-haired grandma," which is just … ouch. Well, I like your hair, Marie.
We'll find out if Callie and Marie broke out the nukes at some point on July 21, which is when Splatoon 2 hits the Switch.