Justice Akatsuka, known to most by his nickname Seigi, is the central protagonist of his narrative. His given name, Seigi, is the Japanese word for justice, and this concept serves as the core of his identity. Raised from childhood in the Akatsuka-style of jujitsu by his enthusiastic grandfather, Seigi is a highly capable martial artist even before the story's supernatural events begin. His sense of right and wrong drives him to protect those who are weaker, a trait that directly leads him into the story's conflict.

Seigi's life changes dramatically after he defends a homeless man, Professor Wiseman, from a group of thugs. As a reward for his kindness, the professor gives him a powerful and mysterious tattoo known as a Power Crest, branded onto his palm. This particular tattoo is named Void Maker, and it is considered one of the most powerful known crests of its kind. Void Maker grants Seigi the ability to create miniature black holes, or voids, which can instantly swallow anything in their path. Unlike many other Power Crests, Void Maker is trigger-less, meaning it does not require a specific condition or action to activate its power. However, the tattoo has a mind of its own and is known to crave blood, making it difficult for Seigi to fully control at times. Beyond its offensive capabilities, Void Maker also allows Seigi to regenerate from injuries.

As a person, Seigi is complex. He can be kind and good-natured, but he also has a capacity for violence when fighting for a cause he believes is right. His motivation is consistently rooted in his powerful sense of justice, compelling him to act against what he perceives as evil or wrongful. Throughout the series, he is pulled into a dangerous international conflict between a special U.S. Army unit and the Kingdom of Selinistan, both scrambling to collect these powerful tattoos. Within this conflict, Seigi becomes a partner to Bluesy Fruesy, often called Izzy, a U.S. Army lieutenant whom he vows to protect. His childhood friend, Tōko Ichinose, also plays a significant role in his life as a close companion who harbors romantic feelings for him.

Seigi's journey is marked by extreme hardship and significant physical trauma, yet his defining trait is his refusal to give up. This perseverance was instilled in him by his father, who taught him to keep trying even when his efforts seem in vain. Seigi holds his father in high regard, believing he died for a just cause. He also treats his grandfather, his martial arts master, with deep trust and respect. Over the course of the story, Seigi suffers devastating injuries in battle, including losing his right arm, both legs, and even his vision. Despite these immense disabilities, he demonstrates an unyielding will to continue fighting, refusing to let his setbacks define or defeat him. This development showcases a progression from a skilled but relatively ordinary high school student into a battle-hardened warrior whose spirit remains unbroken despite being physically shattered.