Eva is a ten-year-old identical twin from Portz, Romania. Her outspoken and fiercely independent nature often leads to clashes with her traditional father but proves vital for her physical endurance in the concentration camp. She relies on her wits, strict mental compartmentalization, and an unbreakable bond with her sister to survive the horrors of being an experimental subject. She continuously demonstrates a rebellious streak by organizing extra food and refusing to show pain to her captors.

Miriam is Eva's identical twin sister, sharing a deep and sustaining connection with her sibling. Placed into solitary confinement and subjected to harmful medical injections, she relies heavily on Eva for physical and emotional support when her own health deteriorates. Her physical vulnerability drives much of her sister's resistance within the camp environment.

An SS physician at Auschwitz-Birkenau, Dr. Mengele is known as the "Angel of Death" for his role in directing prisoners to forced labor or the gas chambers. He operates a specialized program conducting cruel, pseudoscientific experiments on twins in an attempt to advance racial ideology. He maintains a chillingly composed, elegant demeanor that masks his methodical brutality.

Mrs. Csengeri is a Jewish mother from the Mozes family's home region who manages to stay near her twin daughters inside the camp. She acts as a vital source of maternal strength and mutual aid, organizing resources and smuggling food to those in need. After liberation, she assumes a surrogate guardian role for Eva and Miriam.

A former German SS physician stationed at Auschwitz, Münch is one of the few doctors acquitted of war crimes due to his actions helping prisoners. He later serves as a critical figure in Eva's pursuit of historical documentation, signing a formal affidavit to confirm the camp's operations and participating in her public statements of personal peace.

A collective group of roughly 1,500 pairs of twins, primarily Jewish and Romani children, selected for pseudoscientific racial research. They form a unique micro-community within the camp walls. Older children often shelter younger ones, establishing specific rules for endurance and sharing scarce resources to sustain one another through relentless medical procedures.

Known as the "accountant of Auschwitz," Gröning is a former low-ranking SS functionary responsible for processing the belongings of murdered prisoners. His later trial becomes a significant public stage where Eva puts her personal philosophy into practice, interacting with him directly in the courtroom and advocating for educational service.

Alexander is Eva and Miriam's father, a traditional and religious Jewish man who initially clashes with Eva's outspoken nature because he desired a son. He tries to protect his family by enduring the mounting prejudice around them, hoping that their remote location will keep them safe from geopolitical threats and the growing fascist movement.

Jaffa is Eva and Miriam's educated, generous mother who takes pride in her family and community. She refuses early opportunities to emigrate, unwilling to uproot her children or abandon her ailing mother, a decision that deeply impacts the family when they are eventually forced into a ghetto.

Edit is one of Eva and Miriam's older sisters, known in the family for her kindness. She is separated from the twins during the chaotic selection process upon their arrival at the concentration camp.

Aliz is Eva and Miriam's older sister, recognized for her artistic abilities, green eyes, and black hair. She, alongside Edit and her parents, is torn away from the twins on the Auschwitz platform and forced into a different group.

Aunt Irena is Alexander's youngest sister and a Holocaust survivor who takes Eva and Miriam into her apartment in communist Romania. While she provides them with essential shelter and occasional matching clothing, she offers little emotional affection, leaving the girls feeling out of place in her home.

Uncle Aaron is Alexander's brother who emigrates to Palestine before the war. He later corresponds with his nieces and welcomes them when they finally immigrate to Israel, providing them with their first genuine sense of familial affection in years.

Mrs. Goldenthal is a fellow survivor and mother who travels back toward Romania alongside Eva, Miriam, and Mrs. Csengeri. She successfully hid her young daughter, Margarita, under her skirt during their imprisonment, while her twin sons were subjected to medical experiments.

Shmilu is Eva and Miriam's cousin and the sole survivor from his immediate family. After the war, he lives in the summer kitchen of the Mozes farm, working the land and caring for their mother's dog before eventually leaving the village with the twins.

Luci is a Christian minister's daughter and a childhood friend of the twins. She silently watches the Mozes family being marched away from their home, later expressing her childhood sense of powerlessness to intervene against the authorities.

Michael is an American tourist and fellow Holocaust survivor who endured years in Buchenwald and Magdeburg. He meets Eva in Tel Aviv, and despite a language barrier, they quickly connect, marry, and move to Indiana to build a new life together.

Yehudit is one of Rosalia Csengeri's twin daughters from the Şimleu Silvaniei region. She is selected alongside her sister for experimental research but benefits from her mother's persistent efforts to stay nearby and provide for them.

Lea is the other half of the Csengeri twins, subjected to the same grueling medical routines as the Mozes girls. Her survival is aided by her mother's resourcefulness in acquiring extra rations.