Hideki is a 13-year-old Okinawan boy who is conscripted into the Blood and Iron Student Corps just before the US invasion. Issued two delicate ceramic grenades by the Imperial Japanese Army, he is ordered to kill Americans and then himself. He feels paralyzed by fear and believes he is fundamentally incapable of bravery due to a generational curse passed down by a disgraced ancestor.

Ray is an 18-year-old US Marine from a farm in Nebraska participating in his first major invasion. Carrying the psychological scars of growing up with a father traumatized by World War I, Ray notices small humanizing details around him. He struggles to reconcile his combat orders with his conscience when he sees the horrific collateral damage inflicted on Okinawan civilians.

Kimiko is Hideki's outspoken and assertive older sister. She is marked as a yuta—a woman with the ability to communicate with spirits—distinguished by a prominent white streak in her hair resulting from a near-death experience in childhood. Conscripted as a military nurse for the Japanese army, she is fiercely protective of her younger brother and determined to survive the destruction of their island.

Big John is a seasoned, bear-like US Marine and Ray's foxhole buddy. Having chosen the military over juvenile prison, he is a hardened soldier who mentors Ray on battlefield survival. Though he possesses a sympathetic side and comforts Ray after difficult encounters, the brutal realities of combat cause him to display a callous attitude toward the local Okinawan population.

Lieutenant Colonel Sano is a commander in the Imperial Japanese Army. He epitomizes the rigid honor culture of wartime Japan, demanding absolute obedience and glorious self-sacrifice from the newly conscripted child soldiers. He feeds the boys terrifying propaganda about American soldiers to ensure they fight relentlessly rather than surrender.

Oto is Hideki and Kimiko's father. Conscripted into the Imperial Japanese Army as an Okinawan local, he is caught in the crossfire of the invading forces and the defending army. Disillusioned by the military's disregard for Okinawan lives, he deeply regrets that his family was separated during the chaotic evacuation efforts.

Masako is a high school student from Naha who is conscripted to work as a nurse in a horrific field hospital. She endures immense stress as medical supplies dwindle and the violence escalates, ultimately fleeing the collapsing Japanese defensive lines alongside Hideki.

Yoshio is an older student and a notorious bully in Hideki's class. He uses his physical size to intimidate others and fully buys into the aggressive militarism promoted by the Japanese commanders, mocking Hideki for his apparent cowardice during the invasion.

Norio Kojima is the principal of Hideki's school. He is fiercely devoted to the Japanese Emperor, taking it upon himself to physically carry and protect the framed photographs of Emperor Hirohito across the active battlefield, believing the images contain the ruler's spirit.

Sergeant Meredith is the pragmatic leader of Ray's Marine squad. He focuses on keeping his men alive and maintaining order, attempting to minimize unnecessary civilian casualties while aggressively pushing his unit inland.

Private Zimmer is a US Marine in Ray's squad. He is abrasive, highly insensitive, and often clashes with the rest of the unit. His poorly timed pranks and lack of discipline create dangerous friction among the soldiers.

Shigetomo is Hideki's ancestor who surrendered to invading Japanese samurai 350 years prior. According to local Okinawan spiritual beliefs, Shigetomo's restless spirit haunts Hideki, burdening the boy with a legacy of cowardice that he desperately wishes to overcome through military service.

Private Maeda is a Japanese soldier who has abandoned his post to hide underground. Extreme paranoia and fear cause him to view any Okinawan who speaks the local dialect as an American spy, making him dangerously volatile to the civilians he is supposed to protect.

Tanaka is a military photographer for the Imperial Japanese Army. He toured Okinawa to document the island's defense preparations, taking the time to teach a young Hideki how to frame a picture using his fingers to form a rectangle.