Tavia is a high school junior living in Portland. As a Black girl who is secretly a siren, she keeps her mythological identity hidden due to extreme societal prejudice and her father's fears. She communicates via American Sign Language when her suppressed voice burns her throat, claiming to have spasmodic dysphonia to avoid suspicion. She is observant and deeply empathetic, relying on her close circle for support while wrestling with the injustice of her required silence.

Effie is a high school junior who moved in with Tavia's family after surviving a traumatic past incident at Triton Park. She suffers from mysterious symptoms like chronically dry skin and moving hair, leading her to suspect she might be a mermaid. She plays a mermaid named Euphemia at the annual Renaissance Faire, which serves as a vital connection to her late mother and a safe space to explore her identity.

Wallace is an easygoing and reliable lifeguard who works at the community pool Effie frequents. He frequently initiates polite conversations with her and shows genuine interest in her life outside the water. He stands up for Effie when others bother her and demonstrates a surprising knowledge of Black history and social justice movements.

Naema is a high school student and an eloko, a revered mythological being possessing an enchanting, melodic presence. She leverages her high social status to her advantage and frequently clashes with Tavia and Effie. Though she occasionally stands up against racial microaggressions, she prioritizes her eloko privilege over solidarity with sirens.

Camilla Fox is a famous Black hair model and influencer whose online videos provide Tavia with a comforting escape from reality. She later leverages her substantial platform for social justice activism, speaking at protests to defend Black and mythological lives. She acts as a catalyst for Tavia's own personal growth.

Rodney is Tavia's father, a man driven heavily by his fear of society's prejudice against sirens. He strictly monitors Tavia's media consumption and enforces her silence, believing secrecy is the only way to protect her life. His severe approach often makes Tavia feel invisible and creates a massive emotional barrier between them.

Geneva is Tavia's mother, who provides a quieter presence in the household compared to her husband. She often avoids direct confrontation with Rodney regarding his strict rules for Tavia, though she harbors her own concerns about the emotional toll of constant fear. She eventually expresses regret for her passivity.

Mama Theo is Effie's great-grandmother, who originally raised Effie's mother, Minerva. She sent Effie to live with the Philips family for unstated protective reasons. She guards deeply held secrets regarding Effie's father and her mysterious condition, believing that silence will keep her great-granddaughter safe from harm.

Paw Paw is Effie's great-grandfather, providing a gentle and steady presence in her life. Unlike his wife, who often takes a harsh or secretive approach, he offers Effie physical comfort and quiet reassurance when she feels overwhelmed by her lack of answers.

Priam is an eloko and Tavia's ex-boyfriend. He comes from a police family and once shared a romantic connection with Tavia, though he abruptly ghosted her after a misunderstanding involving eloko mythology. His current relationship with Naema adds tension to Tavia's social circle.

Isabella is an empathetic classmate of Effie and an eloko. Unlike Naema, Isabella uses her revered status to respectfully question prejudiced assumptions in the classroom, specifically defending sirens. She partners with Effie for a school project and treats her with genuine concern.

Elric is a high school varsity lacrosse player who portrays the blacksmith's son at the annual Renaissance Faire. In the Faire's storyline, he is deeply in love with Effie's mermaid character, Euphemia. He maintains strict character boundaries, speaking in old-fashioned language and separating his Faire persona from his real-world identity.

Minerva is Effie's deceased mother. She played a pirate captain at the Renaissance Faire, making the event a cherished, safe space for her and Effie. She died when Effie was young and kept the identity of Effie's father a strict secret from everyone.

Gramma is Tavia's deceased grandmother and a fellow siren. Rodney kept her separated from Tavia while she was alive due to his fear of their shared mythological traits. Her spirit resides in the indigo waters, where she passes down ancestral knowledge and ancient siren songs to Tavia.

Rhoda Taylor is a recently murdered Black woman whose tragic death becomes a national media spectacle. Her boyfriend claims she was a siren who used her voice to force him to kill her. Her high-profile trial sparks intense racist discussions and major social justice protests throughout Portland.