Robbie is Sierra's school crush, a quiet and artistic boy. He reveals himself as a shadowshaper and helps Sierra learn to use her powers. Robbie becomes a trusted friend and love interest as he supports Sierra in her journey.

Grandpa Lázaro is Sierra's grandfather who has suffered a stroke, limiting his ability to communicate. He occasionally breaks through to warn Sierra about her powers and upcoming threats. Lázaro has a complicated past with shadowshaping and has made choices requiring redemption.

María is Sierra's mother, a schoolteacher who inherits shadowshaping powers but rejects them. She fears others viewing her cultural beliefs as strange. Through Sierra's encouragement, she begins to embrace her heritage by the novel's end.

Juan is Sierra's older brother and a shadowshaper, using his musical skills for shadowshaping. Protective of Sierra, he eventually supports her by fighting alongside her and helping find the Lucera.

Dr. Wick is an anthropologist from Columbia University who initially studies shadowshaping with good intentions but becomes power-hungry. He targets shadowshapers, including Sierra, using cultural appropriation for his gain.

Mama Carmen, Sierra's grandmother, passed away before the story begins. She shared a close bond with Sierra and previously held the mantle of Lucera, passing on a legacy and connection to ancestors.

Manny, a neighborhood fixture known for his humor and newspaper, is a family friend and shadowshaper who guides Sierra subtly. His death deeply affects Sierra, prompting her to honor him in her artwork.

Bennie is Sierra's best friend, loyal and supportive, despite personal losses. She stands by Sierra during her shadowshaping journey, risking her life to help Sierra achieve her destiny.