Justice Akatsuka, often called by his nickname Seigi, is the central protagonist of the story. A high school student trained from a young age in martial arts by his grandfather, Justice is characterized by a deeply ingrained and almost literal sense of what is right, a trait reflected in his nickname, which means justice in Japanese. This strong moral compass, however, is not simple; his personality can be complex, shifting between a naturally kind and good-hearted disposition and a more violent and aggressive side, though he fundamentally always fights for what he believes is right.

Justice's journey begins when he intervenes to save a mysterious old man from a group of thugs. As a token of gratitude, the man gives him a strange stone that imprints a powerful and unique tattoo called Void Maker onto Justice's palm. This event thrusts him into a hidden conflict involving powerful tattoo users, including a girl named Bluesy Fluesy who confronts him about the origin of his new ability. Void Maker is considered one of the most formidable known tattoos, granting him the power to create miniature black holes or voids that can instantly swallow anything in their path. It is a "trigger-less" tattoo that does not require a specific action to activate, but it is known to crave blood rather than a material like chalk, which powers Bluesy's tattoo. The tattoo also possesses a will of its own, making it difficult for Justice to control at times.

In the story, Justice is recruited by an American military group, partly due to the immense power of his Void Maker. His role evolves from a reluctant participant to a determined fighter, especially after a personal tragedy. He develops strong key relationships, most notably with Bluesy Fluesy, who becomes both an ally and a love interest. His grandfather is a significant figure, acting more as a martial arts master who instilled in him the belief that justice without strength is meaningless. The death of his father, who he believes died for a right cause, also fuels his dedication and fighting spirit.

Justice undergoes significant development, much of it driven by loss and the influence of other characters. After witnessing the death of his close friend and childhood companion, he is consumed by a desire for revenge against the powerful Princess Aryabahta. He undergoes intense training, and through the memories of a veteran fighter named Brad Blackstone, he integrates advanced combat planning and skills into his own martial arts repertoire, becoming a formidable opponent even among tattoo users. A pivotal part of his development is learning that focusing solely on revenge artificially caps his power; a tattoo's true strength thrives on altruism and a selfless will. In a final battle, by offering to sacrifice his own life for Bluesy, he finally taps into his full potential and overcomes his limitations. This reveals that his core motivation, despite his struggles with anger, is ultimately rooted in a desire to protect others and do what is right. Beyond his tattoo, Justice is a highly capable martial artist, having studied Akatsuka-style Jujitsu, and for years, the only people who could best him in a fight were his grandfather and later Bluesy.