Grace is a 16th-century mariner and the eventual chieftain of the O'Malley clan in western Ireland. She possesses a supernatural connection to the sea known as the "Sense," allowing her to predict violent weather. Rejecting the restrictive gender conventions of her era, she trains in knife-fighting, secures control over her family's fleet, and actively defends her coastal territories. She routinely negotiates with rival Irish clans and English authorities to protect her family's autonomy.

Sir Richard Bingham serves as the ruthless English Governor of Connaught. He enforces English law with extreme prejudice, viewing his military position as a mandate to crush Gaelic culture entirely. He holds a bitter, decades-long vendetta against Grace, seeing her continued independence as a direct insult to his authority.

Richard is the younger son of The MacWilliam, chieftain of the powerful Bourke clan. Left-handed like Grace, he trains her in combat and treats her as an equal, standing apart from the violently patriarchal men in her life. His dedication to Grace anchors her emotionally during periods of intense political instability.

Eóin is the formidable chieftain of the O'Malley clan. He possesses the supernatural "Sense" and recognizes the same trait in his daughter, yet he feels intense pressure to enforce standard Gaelic gender roles. He makes calculated decisions to divide his legacy, securing the clan's terrestrial and maritime interests through his children.

Donal is Grace's half-brother and the recognized heir to the O'Malley chieftaincy. He despises the sea and prefers playing music on land, securing his descriptive nickname. He remains entirely loyal to Grace, actively supporting her command of the fleet while he oversees the clan's inland business.

Maeve is Grace's mother and a highly observant presence in the O'Malley household. She holds no illusions about the patriarchal society they live in and teaches Grace that respect must be forcefully taken rather than requested. She continuously advocates for Grace's maritime education.

Queen Elizabeth is the monarch of England, directing the colonial expansion into Ireland from her court. She proves to be highly intelligent and politically shrewd. During her direct interaction with Grace, she demonstrates a practical respect for another female leader surviving male-dominated power structures.

Tibbot is the youngest son of Grace and Richard Bourke. Raised entirely within the violent realities of clan warfare and English encroachment, he inherits his mother's supernatural ability to predict weather patterns. He stands as a symbol of the future that his parents fight to secure.

Finola is the mother of Richard Bourke and a ruthless political operator within the Bourke clan. She leverages her position in the household to manipulate clan alliances and secure her son's path to leadership, showing no hesitation in treating younger women like Grace as expendable political capital.

Donal is a pugnacious chieftain's son and Grace's first husband. He firmly believes in absolute patriarchal control, keeping Grace confined to the castle grounds and restricting her access to the water. His violent temper and frequent disputes make him a dangerous presence in his own home.

Young Eóin is the first son born to Grace and Donal O'Flaherty. Named after his maternal grandfather, he grows up in a dangerous environment shaped by internal clan violence and the steady encroachment of English military forces.

Margaret is the only daughter of Grace and Donal O'Flaherty. She is raised to understand the complex political landscape of 16th-century Ireland and eventually marries into the Bourke clan to solidify a regional alliance.

Merrick is a son of Grace and Donal O'Flaherty. As he matures, he develops deep-seated resentments regarding his heritage, feeling that he has been denied his rightful position as an O'Flaherty chieftain and acting out of a bitter desire to claim power.

Finn is one of Grace's most fiercely loyal guards. He devotes his entire life to protecting her and executing her military commands, viewing her as the rightful leader long before she holds official titles.

Murray is Finn's twin brother and a highly capable guard in Grace's service. He actively participates in her defensive military actions and remains a steadfast presence in her forces throughout her rise to power.

Gutty is a servant who forms an early bond with Grace after witnessing her mistreatment at Bunowen Castle. He grows into a deeply trusted member of her household, reliably gathering information and assisting her throughout her life.

Nora is the unacknowledged daughter of The MacWilliam. Though she works within the tower house, her secret lineage allows her certain privileges. She becomes deeply romantically entangled with the visiting O'Malley heir.

David Bourke holds the title of The MacWilliam, serving as chieftain of his clan. He oversees a busy household filled with political hostages and heirs, managing the complex succession issues that plague his own family line.

Walter is the eldest son of David Bourke and the recognized heir to The MacWilliam title. He displays a profound sense of entitlement and frequently acts aggressively toward those he views as beneath him.

John is the brother of Sir Richard Bingham and a direct enforcer of English colonial policy. He executes brutal military actions against the Irish clans, demonstrating the same ruthless disregard for local lives as his brother.

Richard "Hook" Bourke is the chieftain of the Bourke clan and Grace's son-in-law. He assists Grace in managing salvaged goods and securing mercenaries to defend their combined territories from English forces.

Aisling is the mother of Donal O'Malley and resides in a cottage on Clare Island. She harbors deep resentment over her social position and fiercely guards her son's interests against any perceived slights from the main O'Malley household.

Ultan is Grace's pragmatic first mate. He oversees the daily operations of her fleet and personally accompanies her on dangerous diplomatic missions, demonstrating unwavering loyalty even when he doubts her supernatural instincts.