Simi is a Mami Wata, a mermaid created by the sea goddess Yemoja to gather the souls of those taken by slave ships and return them to the creator. Unlike the other Mami Wata, Simi retains scattered memories of her human life and often feels torn between her aquatic duties and her lingering human desires. When she makes the fateful choice to rescue a living boy from the ocean, she unknowingly breaks a divine decree, forcing her to travel on land in human form to seek forgiveness.

Kola is the son of a village leader who survives a deadly encounter at sea only through Simi's intervention. As a natural protector, his primary motivation is to return home and ensure the safety of his younger twin siblings. He is brave, fiercely loyal to his community, and deeply appreciative of Simi's sacrifices, though his confident upbringing occasionally clashes with the supernatural dangers he faces.

Yemoja is the powerful Orisa of the sea and the creator of the seven Mami Wata. She bears deep facial scars inflicted by the trickster god as punishment for her past actions. She acts as a strict but caring mentor to Simi, warning her of the severe consequences that follow interference in human lives and enforcing obedience to divine decrees.

Esu/Ifedayo is the trickster Orisa and Olodumare's designated messenger, holding dominion over crossroads and misdirection. He operates with a deep sense of arrogance, frequently twisting divine orders to serve his own jealousy and ambition. His selfish refusal to perform his duties correctly threatens the spiritual balance, forcing the main characters into a direct confrontation.

Olodumare is the supreme creator within the Yoruba spiritual system, utilizing "they" pronouns. They established the fundamental laws governing humans and Orisas, particularly the decree forbidding divine interference in mortal lives. Although physically distant from the immediate events, Olodumare's rules dictate the boundaries that all characters must operate within.

Yinka is a skilled young warrior from Kola's village who sports a shaved head and a relentless fighting spirit. She grew up alongside Kola and initially treats Simi with suspicion before bonding with her through combat practice. She is fiercely independent, completely unapologetic about who she is, and willing to risk her life to defend her friends against supernatural threats.

Issa is a yumbo—a silver-haired, child-like fairy spirit drawn to fertile lands and natural vitality. He happily attaches himself to Simi and Kola's traveling party, eager to serve as a guide. His cheerful demeanor and comfort with his own identity provide moments of levity and sincerity during the group's darker trials.

Bem is a dedicated warrior from Kola's village who acts as the primary peacekeeper within his social circle. His name translates to "peace," a trait he frequently embodies by de-escalating arguments and maintaining a calm demeanor under stress. He readily joins the dangerous expedition out of pure loyalty to Kola and their community.

Folasade is an older Mami Wata who crosses paths with Simi early in the story. She represents a strict adherence to the mermaids' purpose, advising Simi against holding onto human memories. Folasade accepts her existence without complaint, serving as a contrast to Simi's ongoing internal conflict.

Simi's parents appear exclusively in her restored memories but deeply influence her actions. Her father taught her how to handle weapons and defend herself, while her mother served as the principal storyteller of their city. The lessons and cultural tales they passed down provide Simi with critical knowledge for surviving her present journey.

Taiwo and Kehinde are Kola's younger twin siblings who serve as the physical embodiments of the Ibeji Orisas. Because of their unique mystical abilities, their presence is vital to the fertility and health of their homeland's soil. Taiwo is naturally daring, while Kehinde approaches situations with caution, but both share a powerful bond that attracts the attention of dangerous supernatural forces.

The Babalawo is a highly respected high priest loyal to Yemoja who resides in a hut adorned with artwork depicting the Mami Wata. He holds critical knowledge regarding the divine rings required to communicate with Olodumare. He serves as a crucial source of information, explaining the severe consequences of the twins' disappearance to Simi and her companions.

Aissa is the leader of the bultungin, a group of shape-shifting werehyenas bound to protect the trickster god's island. She can hold her human form longer than her peers, indicating her strength and status within the pack. Aissa is highly protective of her kind and operates strictly according to the magical bonds that dictate her people's actions.

Sango is the Orisa of thunder and lightning who patrols the ocean alongside his wife, actively destroying slave ships. He disobeys Olodumare's non-interference decree because he refuses to ignore the desperate prayers of his captive people. He is an intimidating, powerful force committed to violently disrupting the traders' operations.

Oya is the Orisa of storms and wind who assists her husband Sango in dismantling the slave trade at sea. She possesses a sharp, observant nature, immediately recognizing Simi's supernatural necklace and offering crucial warnings about the pursuit of the divine rings.

Olokun is the Orisa who oversees the domain of the dead in the deepest parts of the sea. Due to his past attempts to flood the world, Olodumare chained him to the ocean floor, leaving him bitter and isolated. He possesses immense power and strikes a desperate, dangerous bargain with Simi when she seeks assistance.

Kola's parents are the leaders of their local village, carrying the heavy burden of guiding their people through a supernatural agricultural crisis. They love their children deeply and immediately accept Kola's friends into their home without concern for social status. They maintain a dignified but sorrowful presence while believing their younger twins are lost.