Julia is a seventh-grade Korean American student living in the mostly white town of Plainfield, Illinois. She frequently experiences discomfort regarding her heritage due to past encounters with racial slurs and peers' disgust toward traditional foods like kimchi. She prefers hands-on activities like construction or hand-sewing over reading research. Her mother's suggestion to raise silkworms for a state fair project causes her significant anxiety, as she worries the idea is "too Korean."

Patrick is a white middle school student from a large family of mixed Western European descent. He lives down the street from Julia and spends considerable time at her house, where he happily consumes bowls of kimchi and rice. He is an ambitious bookworm who takes charge of the research and planning for their Wiggle Club project, hoping to win a prize at the state fair.

Mr. Dixon is a retired Black widower who lives on Orchard Drive. He drives a distinctive 1970s green Ford LTD and maintains a lush garden. As the owner of the only known mulberry tree in Plainfield, he becomes an essential contact for Julia and Patrick's silkworm project. His children and grandchildren live far away, leaving him eager for company.

Mrs. Song is a Korean immigrant and mother to Julia and Kenny. Drawing on her childhood memories of sericulture in Korea, she suggests raising silkworms for the Wiggle Club project. She possesses a specific set of traditional skills, including the ability to sew perfectly symmetrical Korean embroidery. She holds complex, underlying prejudices regarding certain racial groups, which creates silent tension with her daughter.

Kenny is Julia's seven-year-old brother. He operates as an annoying younger sibling in Julia's eyes, frequently goading her during family meals. He deeply admires Patrick and wants to be included in the older children's activities, demonstrating a surprising capacity for logical observation when allowed to participate.

Ms. Park serves as a stand-in for the author, appearing in brief conversations interspersed between the regular narrative chapters. She listens to Julia's complaints about the direction of the plot and explains the mechanics of storytelling. She draws on her own experiences as a Korean American raised in Illinois to help shape Julia's world.

Mr. Maxwell is a farmer and the adult mentor for the Work-Grow-Give-Live! (Wiggle) Club. He is highly passionate about agriculture and runs a sustainable farm where he rotates cows, chickens, and sheep to keep the land fallow and healthy. He encourages the children to incorporate sustainable practices into their own projects.

Mr. Song is a Korean immigrant and the father of Julia and Kenny. He moved the family to Plainfield two years prior. He acts as a steady presence in the household and willingly assists Julia when she asks him to help drive around looking for Mr. Dixon's specific car.