Werner Pfennig is an 18-year-old who rescues Marie-Laure during the siege of Saint-Malo. His interest in science was spurred by broadcasts during his childhood. He attends a Reich-sponsored school and is influenced by his experiences there and his friendship with Frederick.

Daniel LeBlanc, Marie-Laure's father, works as a locksmith at the French National Museum of Natural History. He is instrumental in Marie-Laure's upbringing, teaching her Braille and crafting puzzles to help her learn and navigate the world.

Jutta, Werner's sister, shares his intelligence and creativity. Together, they build a wireless radio and listen to broadcasts that expose German atrocities, leading Jutta to question the government from a young age.

Etienne LeBlanc, Marie-Laure’s great-uncle, overcomes his fears and becomes a key figure in Marie-Laure’s life, helping her during the siege of Saint-Malo and continuing resistance work after Madame Manec's death.

Madame Manec is influential in Marie-Laure’s life, encouraging resilience and involving her in resistance activities. Her teachings prepare both Marie-Laure and Etienne for future challenges.

Frederick, Werner’s friend and fellow student at Schulpforta, stands out for his intelligence, love of birds, and conscience. Despite facing severe bullying, he leaves a lasting impact on Werner’s values.

Frank Volkheimer is a large and formidable presence, yet gentle to Werner, whom he befriends at Schulpforta. Later, as a soldier, he continues to protect Werner from the brutal realities of war.

Von Rumpel is fixated on finding the Sea of Flames due to his terminal cancer, symbolizing man's greed and self-interest during the events surrounding the war and the search for the gem.