Crow is a mysterious entity and the primary antagonist of the series, serving as the mastermind behind the Alone's attacks on Earth. Despite its name and avian appearance, Crow is not a simple animal or human. It is an Eldritch Abomination, a being that originates from a higher dimensional plane and has existed for an immense span of time, having destroyed countless worlds before arriving at Earth.

In terms of personality, Crow is cruel, manipulative, and deeply malevolent. It acts as a Bad Boss to its primary agent, Rei Kuroki, showing no loyalty or compassion. Crow's first significant action in the story is to inflict magical torment on Rei as a punishment for saving a child from danger, demonstrating that it values adherence to its destructive mission over any act of kindness or morality. Crow possesses a god-like superiority complex, especially after acquiring new powers later in the story, and it mocks the concept of other worlds being anything more than statistics in its mission.

Crow's primary motivation is to ensure the destruction of the Manifestation Engine, the advanced power source that sustains human society. However, its goals are even more total and cynical than they first appear. While it promises Rei that she can restore her lost world and bring back her deceased parents by assisting the Alone, this is purely a manipulative lie. Crow reveals that the higher powers it serves have decided no one should control the Manifestation Engine, and it has no intention of allowing Rei to achieve her personal goals, as it does not want anyone to have access to such technology.

In the story, Crow acts from the shadows for most of the series, communicating directly only with Rei to give her orders and enforce compliance. It physically manifests as a crow that perches near Rei and can cause a mark on her neck to flare up, inflicting unbearable pain as a disciplinary measure whenever Rei contradicts the mission or shows independent humanity. Crow is the force that directs the Alone, the alien creatures that the heroines fight, though its true nature is separate from them. Crow reaches the peak of its role in the finale, where it consumes the arrows Rei had been firing, granting it immense power. It then absorbs Rei entirely, transforming into a colossal, rampaging leviathan perched atop the Manifestation Engine, posing a world-ending threat.

The key relationship is between Crow and Rei Kuroki. This is a classic Deal with the Devil scenario. Crow acts as a manipulative tormentor, holding the false promise of resurrecting Rei's family over her head while physically abusing her for any failure or act of defiance. Despite Crow's threats that it could kill Rei for her continued failures, Rei ultimately challenges it, implying that it might not be capable of such a direct execution. The relationship culminates in Crow absorbing Rei into itself, a betrayal that represents the ultimate act of its cruelty.

Regarding development, Crow does not undergo a moral change or redemption. Instead, its transformation is purely one of power and escalation. It begins as a hidden, manipulative force, but after consuming Rei's arrows, it gains enough power to physically manifest as a gigantic, rampaging monster capable of planetary annihilation, shedding its subtle guise for direct destruction.

Crow possesses several notable abilities. It can teleport or move unseen, appear as a small crow, and directly cause pain to Rei through a magical mark. Its most significant power is its ability to consume or absorb others and energy to enhance itself, as shown when it consumes Rei's arrows and later Rei herself to become a massive, powerful creature. In this enhanced state, it becomes a leviathan-class monster that poses a direct threat to the entire planet. Furthermore, as a higher-dimensional being, Crow perceives reality in a way that is fundamentally different from humans, and its true form is not constrained by normal physical laws.