Ebony-Grace is an imaginative 12-year-old girl from Alabama who possesses a deep love for science fiction, outer space, and superheroes. She uses her vivid imagination to cope with changes in her life, often turning real-world situations into epic space battles involving her alter ego, Space Cadet E-Grace Starfleet. Relocating to Harlem for the summer, she initially views her new bustling environment as a hostile planet.

Jeremiah Granville Norfleet is Ebony-Grace's grandfather and a former engineer who became one of the first Black men to work for NASA. He lives in a large house in Huntsville, Alabama. He provides his granddaughter with the foundational stories and vocabulary she uses to understand her life, blending funk music references with science fiction.

Julius Freeman is a working-class man who owns an auto repair shop, a junkyard, and a brownstone in Harlem. He acts as a pillar in his community, helping those in need and organizing local events like block parties. He wants his daughter to maintain her unique personality while learning to participate in the real world rather than constantly retreating into fantasy.

Bianca is a neighborhood girl who lives with her grandmother on the ground floor of Daddy's brownstone. She loves breakdancing, rapping, and jumping double-Dutch, aspiring to be a famous performer. While she used to play outer-space games with Ebony-Grace when they were younger, she now prefers the vibrant street culture of her Harlem community, leading to friction between the two girls.

Gloria Norfleet is Ebony-Grace's proper, strict mother living in Huntsville, Alabama. She intensely dislikes New York City, viewing it as dangerous. She worries that her daughter's fixation on science fiction will hinder her social development as she approaches junior high school, preferring she wear frilly dresses instead of space-themed clothing.

Known as "Mint Chocolate Monique," she is the confident, outspoken leader of the Nine Flavas Crew in Harlem. She dictates the group's activities, from double-Dutch to breakdancing, and enforces their style. She possesses a quick wit and frequently points out the differences between her street-smart crew and Ebony-Grace's sheltered demeanor.

Pablo is a talented breakdancer and rapper in Harlem who occasionally goes by the name "Pablo Jupiter." Unlike many of the other kids in the neighborhood, he shares some of Ebony-Grace's interest in science fiction and outer space, blending it into his hip-hop persona. He actively seeks to collaborate with other talented dancers in the community.

Calvin, also known as "Pigeon-Chest Boy" or "Stone-Cold Calvin," is a boastful B-boy in the neighborhood. He holds rigid views about gender roles in hip-hop culture, insisting that breakdancing and rapping are strictly for boys. He acts as an antagonist to the neighborhood girls who want to compete.

Diane is a recent high school graduate in Harlem who takes on babysitting jobs. She wears popular, colorful street styles and acts as a bridge for Ebony-Grace to observe the local culture, taking her to the laundromat, bodega, and local parks.

Uncle Rich is Daddy's younger brother who lives in the Harlem brownstone. He maintains a chaotic personal life, frequently bringing women home, and relies on small bribes to keep his activities quiet. Despite his flaws, he treats his niece's imaginative stories with good humor.

Lester is an unhoused man living in the Harlem neighborhood. He struggles with personal issues and addiction but maintains a respectful relationship with Daddy, who treats him with dignity and provides him with small jobs around the auto shop to earn money.

Señora Luz is Bianca's grandmother and guardian. She is a traditional, strict, but loving woman who cooks homemade meals for her granddaughter and insists on regular church attendance. She treats Ebony-Grace kindly, welcoming her into their routine.