Katie is a resilient, resourceful 12-year-old girl living in New York City with her single mother. Trying to earn money to attend summer camp with her friends, she takes on various odd jobs around her apartment building before landing a highly unusual cat-sitting gig. She is a vegetarian with a strong sense of kindness and responsibility toward animals.

Bethany is Katie's best friend who comes from a wealthier family and is able to attend a four-week summer camp. Over the summer, she develops new interests and begins signing her postcards as "Beth," signaling a shift in her identity. She frequently uses decorated postcards to communicate with Katie while away.

Ms. Lang is Katie's upstairs neighbor who hires the young girl to watch over her staggering 217 highly intelligent cats. She is a dedicated animal rights activist who speaks passionately at protests and serves as an important mentor to Katie. She sees Katie's potential and rewards her dedication with guidance.

Cheryl is Katie's hardworking mother who works long shifts to provide for them. Though the family struggles financially and lives paycheck to paycheck, she strives to be present and emotionally supportive of her daughter. She offers guidance without being overbearing and prioritizes Katie's happiness.

Mr. B owns and operates the bodega located beneath Katie's apartment building. He acts as a warm, fatherly figure to Katie, frequently offering her free groceries, meals, and practical advice. He is a perceptive listener who provides Katie a safe space to talk about her struggles.

The Eastern Screech is New York City's most popular superhero, boasting an owl-themed aesthetic. Despite his immense public adulation and positive Yelp reviews, he frequently misinterprets crime scenes. He focuses more on his public relations brand than actual heroism.

Jess is part of Katie and Bethany's school friend group. She is eager to attend summer camp with Bethany and is frequently teased by her friends for developing rapid crushes on every boy she meets, including local superheroes.

Marie is an active skateboarder around Katie's age with pink hair. She meets Katie at an animal rights protest, and the two quickly bond over their shared interests. She represents a new phase in Katie's expanding social circle.

Mrs. Piper is the building manager of the apartment complex where Katie lives. She strictly enforces building rules, particularly the strict "no pets" policy, which makes her a constant source of stress for Katie while cat-sitting.

Cold Hands is a superhero sidekick who gives tours at the local hero museum. He is eager to promote his own exhibit but becomes frustrated when visitors only care about more famous heroes. He lacks basic athletic skills, as seen when he struggles to climb a simple building.

Police Chief Pardo is the head of the local police force, tasked with investigating a series of attacks on local businesses. He is a pragmatic official who must deal with the chaotic interference of city superheroes during his ongoing investigations.

Scratch-Off is Mr. B's notoriously aggressive bodega cat. While he usually attacks customers and is considered unfriendly by most patrons, he immediately takes a liking to Ms. Lang and Katie when they visit the store.