Eiji Hoshimiya is the protagonist of the story and a high school student living in a world recovering from a catastrophic event known as the Great Destruction. He is a young man with short black hair and light-blue eyes, and he bears a distinct mark of an Order user on his left palm. Several years prior to the main events, a mysterious entity appeared before him and granted him a wish, the consequences of which he believes led to the devastation that claimed countless lives and changed the face of the earth. For ten years, he has lived with this crushing guilt, hiding his identity as an Order user and refusing to wield the immense power he possesses.

As a person, Eiji is characterized by his withdrawn and introverted nature. He is largely indifferent to the world around him, often skipping classes and keeping his distance from his peers, who view him as socially awkward and reclusive. This apathy is a direct result of the trauma he carries; he has deliberately isolated himself to avoid any situation that might force him to confront his past or use his abilities. Despite this detached exterior, he harbors a deep well of guilt and a strong sense of moral responsibility, though it is almost entirely focused on one person. His sole priority and the primary motivation for nearly all his actions is his younger stepsister, Sena, who suffers from a terminal illness. His devotion to her borders on obsessive, and he is willing to risk his own life and even the fragile peace of the world to ensure her safety and happiness. While he generally resists violence and the selfish use of his power, this principle is flexible when her well-being is at stake.

At the beginning of the story, Eiji believes his childhood wish was for world domination, an immature and reckless desire that spiraled out of control and caused the Great Destruction. The power he believes he wields as a result is called Bind Dominator, also known as the domain expansion. This ability allows him to define a territory around himself; within this domain, he possesses absolute control over both living and inanimate objects, able to command anyone or anything with his spoken word. However, this power is not without notable limitations. Its effects can be dependent on the target hearing his command, and its range is initially restricted before it later grows to a planetary scale. This incredible potential to rule everything is something he is deeply afraid of.

However, a central truth eventually comes to light: Eiji's memories have been altered. The real culprit behind the Great Destruction was not him, but his sister Sena. Her vague wish to stay with her family forever caused her own uncontrollable power to go berserk, leading to the disaster. Eiji’s true wish was not for domination, but to absolve his sister of her sin. His genuine Order ability is called Illegal Digger, which allows him to steal the memories and special powers of other Order users. After Sena’s wish caused the Great Destruction, Eiji used Illegal Digger to take her memories of the event and her original, devastating power, the Bind Dominator. He then used the same ability to alter his own memories, implanting the false belief that he was the one responsible. This act of self-sacrifice is the cornerstone of his character, transforming him from a guilty boy into a tragic figure who willingly took on an unbearable burden to protect his sister from her own actions.

Eiji's key relationships are complex and drive much of the story's conflict. His bond with his stepsister Sena is the emotional core of the series, a desperate and unconditional love that he defines his entire existence around. In stark contrast is his relationship with Rin Kurenai, a young woman who initially seeks to assassinate him to avenge her parents, who died in the Great Destruction. Despite her murderous intent, Eiji is immediately taken with her and, in a moment of panic, uses his Bind Dominator to order her to be his companion and not to attack him or his sister. This forced partnership develops into a tentative and volatile bond, with Rin's thirst for revenge slowly softening into something resembling affection, while Eiji grapples with his feelings for someone who is both his greatest threat and most steadfast ally. He also becomes entangled with the Dazaifu government organization, a group of powerful Order users who intend to use him as a figurehead to establish an independent nation. As he reluctantly takes a leadership role among them, he navigates their political machinations and hidden agendas, all while trying to find a way to save Sena. His greatest adversarial relationship is ultimately with his own father, whose hidden schemes and manipulation of his and Sena's wishes set the entire tragic plot in motion.

Throughout the series, Eiji undergoes significant development. He begins as a passive, guilt-ridden recluse, haunted by a past he believes he caused. As the truth of his real wish and Sena's role is revealed, he is forced to shed his false identity and accept responsibility for his actual choice to shoulder his sister's sin. He evolves from a boy trying to hide from the world into a reluctant hero who must actively use his powers to fight against the true conspirators and for the future of the world, not just for his sister. His journey is a constant struggle to reconcile the corrupting allure of absolute power with the desire for atonement and protection, ultimately defining him as a character shaped more by selfless sacrifice than by selfish ambition.