Alcor, also known as the Anguished One, is a central figure whose true name is revealed as 亚鲁·萨达克 in the narrative. His real identity is that of the eighth Septentrion, the North Star's eighth star, known as the Death Star. He is the creator and operator of the Nicaea cell phone application, the very program that allows humans to summon demons and view death clips. Long before the events of the story, he taught the art of demon summoning to the峰津院 family, a powerful clan that plays a significant role in world affairs. His influence on human history is even more profound, as he is the one who gifted humanity with fire, writing, and painting in ancient times, fostering the free potential he saw within them. He bears a sense of responsibility for the current state of the world, viewing its chaos as a consequence of the gifts he bestowed.

Alcor is a being of immense power who always maintains a calm demeanor, often seen with a faint smile that rarely wavers, even in moments of sadness. He has a deep and genuine fascination with human beings, their customs, and their potential. Unlike the other Septentriones, who are mere systems designed to destroy humanity, Alcor is unique in his capacity to feel emotions. This emotional depth initially causes him to question his own existence, wondering if he is simply a mechanism of Polaris, the entity governing their world. He does not see himself as an enemy of humanity; rather, he wishes for the best for them and is driven by a singular purpose: to prove the infinite possibilities that humans possess.

Throughout the story, Alcor appears before the protagonist and his friends, observing their choices and presenting them with trials. He refers to select humans he deems exceptional as shining ones, a title he gives to both the protagonist, Hibiki, and his predecessor, 峰津院大和. His role is neither purely antagonistic nor wholly supportive; he sometimes offers cryptic guidance and aid, while at other times acts as an obstacle, all in service of testing humanity's resolve. His central motivation is to find a human who can prove that free will and potential can overcome a predetermined fate.

Alcor's key relationships are with the two shining ones he has chosen. He has a complex history with 峰津院大和, who rejected the title of shining one in favor of his own ideals. In contrast, he forms a strong bond with the protagonist, Hibiki. Alcor takes everything Hibiki says seriously and comes to value how Hibiki treats him as an actual person rather than a mere tool or system. This relationship is what ultimately convinces Alcor that his will is his own and not a directive from Polaris. He is also the master of the demons Bifrons and Botis, who carry out his orders.

Alcor's development in the story is marked by his growing conviction that he can act of his own free will. In a significant act of defiance against the established system, he chooses to confront 峰津院大和, intending to kill him to entrust the fate of the world to Hibiki. This battle leads to a critical moment where Alcor sacrifices himself, self-destructing to prevent大和 from reaching Polaris. However, his story does not end there, as he later reappears, carrying the memories of the previous seven days, suggesting a form of resurrection.

Alcor possesses a range of notable abilities. He prefers to battle in his human form, where he can summon razor-sharp, tentacle-like wires from his back to use as weapons for both offense and defense. He can also assume his true Septentrion form, a cube with a red and black striped pattern, which provides him with strong defensive capabilities. He is capable of telekinesis and can levitate. In battle, he is known for his signature Ominous Star attack, which inflicts a curse on enemies that causes them to take significant additional damage when struck. His power is such that he is considered the strongest of the Septentriones, and he can even manipulate the molecules of objects, such as making any food taste delicious.