Callie (アオリ, Aori) and Marie (ホタル, Hotaru) are supporting characters in the Splatoon franchise. Together, they make up the Squid Sisters (シオカラーズ, Sea o' Colors) pop duo. They are Inklings, but Marie unlike most inklings has shorter, tied-up tentacles. Despite being called the "Squid Sisters", they are actually cousins.
In the original Splatoon, Callie and Marie are a pair of pop idols who host Inkopolis News, where they announce what stages are available for online multiplayer as well as giving information on updates and Splatfests. During Splatfests, Callie and Marie can be seen in Inkopolis Plaza performing atop trucks, much like their Assist Trophy function, although each Squid Sister has their own truck rather than performing on the same stage. These concerts can also be viewed through use of amiibo.
In Splatoon 2, Callie and Marie's role from the first game is taken by Pearl and Marina of Off the Hook. Marie now hosts the story mode in Octo Canyon, while Callie, kidnapped and brainwashed by DJ Octavio, serves as part of the final boss. However, partway through the boss fight, Marie is able to free Callie from DJ Octavio's mind control. For the final phase of the fight, they perform together on a stage similar to the one seen in Super Smash Bros.. As of the 3.0 update of Splatoon 2, players are able to speak with Callie and Marie in Octo Canyon after completing the final battle, learning statistics about their performance in online multiplayer as well as various tidbits about the characters themselves.
As an Assist Trophy
The Squid Sisters appear collectively as an Assist Trophy character in Ultimate. When they are summoned, they appear in the middle of the stage (teleporting if not there already), and perform a live concert. As they are performing, the camera zooms in on them, and the blast lines get smaller and smaller, making it easier for players to be KO'd, similar to the game's Sudden Death. Once the song finishes, the duo disappears, and the camera returns back to normal.
During the performance, the Squid Sisters will perform one of two songs: Calamari Inkantation or Ink Me Up. Each is accompanied by a unique dance.
Squid Sisters won't appear in stages that render characters in 2D (such as Flat Zone X and Pac-Land). stages with a constant layout change (such as Port Town Aero Dive), and stages with stage hazards that can engulf the majority of platforms (such as Norfair). They will not appear if a fighter is in Final Smash standby, and if a Final Smash is activated during the concert (such as by the Final Smash Meter filling), the sisters will instantly disappear. Players cannot attack them, or climb atop their stage, and players who manage to do so just get knocked off unless they use glitching or hacking, and the Squid Sisters unlike most assist trophies do not pick a 'side', which means attacking the enemy player(s). Rather, they just sing.
As a Spirit
The Squid Sisters appear as a spirit in Ultimate. In their spirit battle, the player (who is easy to launch) battles against 4 Inklings on Moray Towers, as hostile Squid Sister trophies spawn occasionally. The Ink Me Up music track plays during the fight.