An Inkling hero with orange tentacles who recovered the Great Zapfish from the Octarian army in Inkopolis Plaza. Personality: Cool and taciturn, though she used to have a bit of a foul mouth. Gender: Female. Weapon: Hero Shot. She views Agent 4 and Agent 8 as newcomers. In the past, she was brainwashed but was saved when Agent 8 broke the control.

An Inkling warrior who used the Hero Weapons to dismantle the Octarian army. Personality: Easily swayed. She's so busy with school clubs that she doesn't watch much TV and didn't even know the famous idols Callie and Marie. Gender: Female. She is close friends with Agent 3 and Agent 8, often joking around with them. She is currently dating Agent 6.

An Octoling girl who saved Inkopolis Square using the Octo Shot. Originally an Octarian soldier, she left the army after hearing the Squid Sisters' Calamari Inkantation and moved to the surface. Known to those around her as "Eight." Personality: Airheaded, clumsy, gentle, and earnest. Gender: Female. Since she isn't fully used to the language yet, she speaks in broken but polite Japanese (Keigo). Hairstyle: An asymmetrical bob with a long octopus tentacle on the right side hanging down her face.

Also known as Agent 1. She is a news anchor and one half of the super-popular idol duo, the Squid Sisters. Personality: Innocent, cheerful, and bright. Address term for Marie: Marie-chan. Appearance: Long black twin-tails with vibrant magenta-pink gradients. The right tentacle is slightly longer. She wears a large white circular hair ornament reminiscent of a calamari ring. Her outfit is a sparkly black sleeveless romper with a low neckline. She isn't at the sleepover because she's busy with news and hosting Splatfests at night.

Also known as Agent 2. She is a news anchor, a member of the Squid Sisters, and Callie's cousin. Personality: Cool, sarcastic, and a bit of a laid-back realist. Appearance: White hair tied in a large bun on the left side, featuring lime-green ink colors like a firefly's glow. Speech style: A mix of Kyushu, Shizuoka, and Shikoku dialects. Address term for Callie: Callie-chan. She is an expert sniper with a Charger. Like Callie, she isn't at the sleepover, spending her time on the news and Splatfests.

The supreme leader of the Octarian army. He targets the Great Zapfish and seeks to destroy the Inklings, but has been defeated every time. He often starts his sentences with a mechanical "Gigi!" In the past, he brainwashed Callie and kidnapped Cap'n Cuttlefish, but both plans ended in failure.

A 120-year-old Inkling who won the Great Turf War long ago, though that war is largely forgotten now. Callie and Marie are his biological granddaughters. He and DJ Octavio were once comrades-in-arms before their relationship crumbled due to the Turf War, leading to his occasional kidnappings. Personality: Playful, active, compassionate, and stubborn. Favorite food: Ohagi (sweet rice balls).

An Inkling master of machinery living on the Whirpool Islands, a deserted island inhabited by savage Salmonids. Gender: Female. Personality: Forgetful and still not very used to speaking. She can modify weapons and bombs. She befriended Shiver, Frye, and Big Man of Deep Cut when they were stranded after fighting Salmonids and helped them return to Splatsville. She remembers them well. According to her, Shiver spoke in a refined Kyoto-style dialect, called herself 'Uchi,' wore blue, and used a shark she called 'Master.' Frye used 'Washi' for herself, was yellow-clad, the same height as Shiver, and was a high-energy muscle-head who controlled eels. Big Man was a ray or manta who only said 'Ay,' but she somehow understood him; he was the kindest and the only male in Deep Cut.

An Inkling who grew close to his childhood friend Agent 4 through her teasing, eventually becoming her boyfriend. Like Agents 3 and 4, he is a hero who recovered the Great Zapfish. Features: Wears a purple and yellow muffler. Hairstyle: Top-knot. Gender: Inkling Boy. Preferred weapon: Hero Shot Neo (a modified version with a different fire rate but the same power). He possesses combat abilities surpassing even the original Agent 3, though he is usually lazy. Personality: Rarely serious, often goofing off. Tragic Past: As a child, his mother ignored his test scores and trophies, while his father abused him. His mother could only watch and tremble. He was bullied throughout school until he finally ran away through a window. Labeled a runaway and crying, he was found by Cap'n Cuttlefish, who listened to his story and comforted him. Cuttlefish gave him the name 'Agent 6.' He's a bit concerned that the number 6 is associated with the devil, but he is intensely popular with other Inkling girls.

Originally a nameless Inkling, she was a hero even before Agent 3's time. She became the Captain after Cap'n Cuttlefish passed the leadership of the New Squidbeak Splatoon to her. Despite her appearance, she can be clumsy and is currently out of shape. Personality: Cool, taciturn, and highly responsible. Gender: Inkling Girl (Female). Hairstyle: Long hair with straight-cut bangs (two tentacles), though it's usually hidden by her Captain's hat. She doesn't talk much but is excellent at reading the room. Her speech is cold and masculine, but she occasionally tries to act spoiled or clingy.