Rentaro Satomi is a young teenager with a small frame and messy dark blue hair that partially covers his forehead, reaching below his eyes with untidy parted bangs. He has slightly slanted blue eyes with thick eyelashes and thin eyebrows. His hair is unkempt, featuring loose strands with gaps that hover over his brows. Rentaro also has thick sideburns that frame his cheekbones. His small ears, normal-sized feet, and facial features, including a small jawline, thin lips, and slender nose, give him a youthful appearance. Despite his work in dangerous environments, Rentaro shows no visible scars on his body.

Rentaro’s attire typically includes a black suit, which he wears loosely. His jacket, left open with a single button fastened, reveals a light blue interior and features a blue strap running from the collar to the bottom on the right side. The inner collar of the jacket has thin black lines, complementing the strap. Underneath, he wears a white shirt with a large turtleneck, paired with a blue tie. His outfit appears messy, as one side of his shirt is tucked into his pants while the other is left untucked.

For his lower body, Rentaro wears black pants held up by a blue belt adorned with a small white line circling the center. The back of the pants includes two pockets for storing items like his Civil Security license. He completes his look with high black shoes, featuring a lighter-colored sole.

Rentaro Satomi is a compassionate and empathetic individual, known for his deep-seated sense of equality and justice. Despite societal discrimination against Cursed Children, Rentaro treats them as equals, showcasing his kind-hearted nature. This is evident in his unwavering support for Enju Aihara, his partner and a Cursed Child, whom he defends against mistreatment from her school peers. Rentaro’s protective instincts lead him to leave his own school to comfort and stand by her, demonstrating his loyalty and care for those he values

However, Rentaro’s sense of morality is not without its struggles. Under extreme pressure or in situations where he feels powerless, he has been known to act in line with societal prejudices. For instance, he once hesitated to intervene when witnessing a Cursed Child being abused and even pushed her away in a moment of panic. These actions weigh heavily on his conscience, leading to deep regret and a subsequent drive to make amends, such as rescuing the same child after she was left gravely injured.

Rentaro has a volatile temper when it comes to sensitive subjects, particularly regarding his deceased parents. When Kisara Tendo, his childhood friend and close ally, questions his motivations about finding them, Rentaro reacts with intense anger, leaving the conversation abruptly. His unresolved feelings about his past contribute to moments of self-doubt and a lack of confidence in his abilities as a fighter. At times, this insecurity causes him to temporarily abandon missions or question his place within the agency.

Despite these challenges, Rentaro consistently displays a strong resolve when faced with overwhelming threats. His calm demeanor in critical situations allows him to gather the strength needed to protect his loved ones. Rentaro also harbors deep feelings for Kisara, often showing care and concern for her, hinting at a romantic affection that underscores their close bond. Through his actions, Rentaro strives to be a protector and advocate for those marginalized by society, embodying a mix of vulnerability, determination, and compassion.

As a Promoter, Rentaro partners with Enju Aihara, an Initiator with enhanced abilities, to combat Gastrea threats and ensure the safety of their city. Their teamwork is a central element of the series, showcasing their mutual trust and effectiveness in battle.

Rentaro’s primary role involves battling the Gastrea, parasitic creatures that threaten humanity’s survival. His enhanced prosthetic limbs, coupled with his combat training, make him a formidable opponent.

Throughout the series, Rentaro confronts the injustices faced by the Cursed Children, striving to protect their rights and challenge societal prejudices. His struggles highlight the themes of discrimination and the cost of maintaining one’s ideals in a broken world.

• Enju Aihara
  Rentaro shares a close and protective relationship with Enju, his Initiator. While they work seamlessly as a team, their bond extends beyond professional duties, with Rentaro acting as a mentor and older brother figure to Enju.

• Kisara Tendo
  Rentaro has a complicated relationship with Kisara, his childhood friend and the leader of the Tendo Civil Security Agency. Their connection is marked by shared history and mutual respect, though Kisara’s darker tendencies sometimes clash with Rentaro’s ideals.

• Tina Sprout
  Initially an adversary, Tina becomes one of Rentaro’s allies after he helps her break free from her circumstances. Their relationship reflects Rentaro’s ability to inspire change in others.

Rentaro Satomi is celebrated as a protagonist who balances idealism with the harsh realities of his world. His resilience, intelligence, and dedication to justice make him a compelling character in Black Bullet. Through his struggles and growth, Rentaro embodies themes of hope, morality, and perseverance, leaving a lasting impact on the series and its fans.