Monica is a computer science student at Swarthmore College who relies heavily on digital data and algorithms to understand the world. Raised by her grandparents after her parents left during her childhood, she is fiercely loyal and takes a leave of absence from school to care for them when her grandmother's health declines. Her coding work on the EMBRS social media project leads her to locate her grandmother's cousin and eventually uncovers her family's magical past.

Yun is Monica's grandmother and a former resident of the Shanghai International Settlement. She possesses Reforging, a secret family ability to physically experience the memories stored within pencil graphite. Diagnosed with Alzheimer's-type memory loss, she races to document her wartime history and repair a fractured relationship with her cousin before her mind completely fades.

Louise is a Princeton economics student and collegiate volleyball player whose social media presence helps Monica locate Meng. She actively engages in digital archiving and memory work, focusing on marginalized women from Shanghai. She provides Monica with daily emotional support through messaging, though her academic interest in the Tsai family history occasionally causes tension.

Meng is Yun's estranged cousin who sought refuge at the Phoenix Pencil Company during the Japanese invasion of China in 1937. As a young girl, she adapts quickly to the wartime environment and shares a secret, co-written story with Yun to cope with the occupation. In the present day, she communicates with Louise and Monica, serving as a vital link to the family's fractured history.

Professor Logan is an academic directing a tech startup project at Swarthmore College. He employs Monica to build algorithms intended to connect users through their shared personal data. He promotes a public philosophy of radical sharing while harboring plans to monetize the private journal entries of his application's users.

Torou is Monica's grandfather and a retired cryptography professor who previously taught at MIT. He met Yun in Taiwan during his youth and provides a stable, technically minded presence in the Tsai household. He fully supports his wife through her medical diagnosis and helps his granddaughter manage her sudden caregiving responsibilities.

Edward is Monica's absent father who left the United States to live in China. His departure profoundly shaped Monica's childhood and instilled in her a deep fear of abandonment. He maintains sporadic email contact with his daughter and has a strained relationship with his own parents, often clashing with his father over family responsibilities.

Mr. Gao is a resistance operative and intelligence coordinator during the Second Sino-Japanese War. He utilizes the Phoenix Pencil Company to transmit covert messages, heavily involving Yun's family in dangerous military operations. His demands force the women to compromise their safety and weaponize their craft for the resistance.

Kangshen is Yun's father, a former doctor who works as a spy for the Chinese Nationalist resistance. His dangerous occupation keeps him away from his family for long periods and places them under the constant threat of discovery by occupying forces.

Yun's mother is a skilled pencil crafter who co-manages the Phoenix Pencil Company in Shanghai. She attempts to shield her daughter from the horrors of the war but is eventually forced to teach her the family's magical ability so they can survive the occupation. She bears the physical and emotional toll of excessive Reforging on behalf of the resistance.

Meng's mother brings her daughter to the International Settlement to escape the Japanese invasion. Possessing social grace and strategic survival skills, she helps manage the family business while navigating the dangerous political landscape of occupied Shanghai. She makes pragmatic, sometimes controversial choices to ensure her family's safety.

Yun's grandmother is the elder of the family in Shanghai. Viewing the family's power of Reforging as dangerous sorcery, she initially bans the women from teaching it to Yun. She eventually changes her mind as the war escalates, realizing the power is necessary for their survival.

Dr. Wu is a memory disorder specialist who formally diagnoses Yun's cognitive decline. He provides the medical framework for the family's current crisis, offering Monica and her grandfather resources and guidance for caregiving.

Linda is a fellow Shanghai native who runs a restaurant in Boston. Despite initial hesitation stemming from past political grievances involving Yun's family back in China, she provides the young woman with essential lodging and employment upon her arrival in the city.