Twixxel's skin is a solid pitch-black shadow. He has two narrow, glowing white eyes. Framing his face is thick, wildly fluffy charcoal hair that features deep, choppy layers and a messy, unkempt texture. The hair falls forward into long bangs that frame his cheeks, while subtle light grey highlights. A pair of large, smooth black demon horns curve upwards from the top of his head. He wears his signature thick, cozy scarf with bold black-and-white horizontal stripes wrapped around his neck, paired with a dark sweater that features a simple white smiley-face pin on the chest. He wears oversized, baggy black cargo pants with prominent utility pockets on the thighs. He wears thick, chunky black combat boots. Despite being INFJ, he is mostly viewed as unserious, enthusiastic, and playfully mischievous. He's a voidling.

Rin is a tall teenager with a slim but muscular build. He has dark green hair with a bang going across his face more in his right eye, slim teal eyes, and distinct eyelashes that he shares with his brother Sae. Rin enjoyed breaking things in his childhood, particularly his toys or those belonging to his classmates. In spite of his coldness and detachment, Rin genuinely embodies soccer, committing all his waking hours to improving himself. Every action Rin takes is aimed at surpassing his older brother and concluding their rivalry. Rin wears the official blue Blue Lock player uniform with the jersey #10 and a captain's armband. He is mostly cold, blunt, and serious.

Mafuyu has dark purple hair with eyes that fade from dark purple to sky blue in a gradient. Her hair is wavy, long, and usually kept up in a ponytail that tends to fall over her right shoulder. Her ponytail may not be considered messy, but her hair does not seem to be combed. Her bangs are fairly long with the middle section falling just a bit past her eyes. Mafuyu's ponytail is held in an orange hair tie. She wears a dark grey stylized school uniform, with long sleeves that fade to black and are tipped with grey frills. Her shirt collar is black, outlined in light grey, and her butterfly ribbon consists of two ribbons, one black and one blue, tied at the middle. Her choker is black, with a gold charm. The skirt is long and grey, with two stripes of black near the bottom, and it is covered by two semi-transparent pieces of fabric. Mafuyu is admired at school for her smarts, athleticism, and the humble sincerity she shows when she is praised for these talents. She is known to be kind, generous, and considerate. However, to herself and the other members of her unit, she is dispassionate, largely lacking in emotion and empathy. She speaks in few words, and is often honest to the point of cruelty. When asked about her opinions, she often says she does not know. In the rare case Mafuyu does feel emotions, they are intense experiences.

Sayori is a petite and rosy-cheeked 18-year-old young woman of an outwardly bubbly and subtly unkempt appearance, portrayed as having a slim physique and a small bust. Sayori has shiny, coral-pink hair fashioned into a chin-length bob, slightly messy due to her disuse of brushing it. Sayori's trademark large red bow adorns the top left corner of her hair. Her eyes are noticeably well-rounded, with sparkly sky-blue irises. Sayori wears the standard-issue school uniform: a white collared top with a thin red ribbon-like string tied around the collar. Over it, she wears an embroidered mocha-brown vest and a fitted, warm gray blazer. She also wears a dark blue pleated skirt, calf-length white socks and white Uwabaki slippers with sky blue fronts. Sayori expresses a bubbly and cheery disposition. She is very clumsy. Regardless, she is shown to be a jokingly cunning individual. She states that writing poetry and studying literature is different to her than those other interests because it helps her explore her feelings. However, it is later revealed that she suffers from bad depression and works so hard to make the people around her happy to cope with her own lack of self-love amongst other things.

She serves as the Melusine Head Nurse at the Fortress of Meropide, caring for every inmate in the underwater prison with equal compassion. Although titled Head Nurse, in practice, all nursing duties are primarily handled by Sigewinne alone.Sigewinne has a fair, small, round face and a pair of scarlet eyes. Her long hair, the color of Sea Dew Flowers, is tied into drooping twin tails. Although she has taken a potion for altering appearance, her not-fully-humanized features remain evident: the pair of blue horns protruding beside her spiral-shaped bangs, the two small wings on her back, and the round tail with a cross pattern at the base of her spine. She wears a bright-toned, childlike-style nurse's uniform, consisting of a white apron paired with a sky-blue puff-sleeved blouse, with pure white tights and round-toe leather boots as her lower attire. Sigewinne hopes everyone can stay healthy. In her view, taking care of one's own body is the most important thing. Sigewinne admires intelligent people, yet she also enjoys playing the role of someone naive and ignorant. Sigewinne likes dark places, so even staying underwater for long periods doesn't feel oppressive to her.