"Big Order" is a ten-episode anime series that revolves around a world where individuals known as "Order Users" possess supernatural abilities granted by mysterious entities. These powers, referred to as "Orders," allow users to manipulate reality in various ways, but they come with significant consequences. The story centers on Eiji Hoshimiya, a high school student who harbors a dark secret: he is an Order User with the ability to destroy the world. His power stems from a traumatic event in his childhood when he wished for the destruction of humanity, resulting in a catastrophic earthquake that devastated Japan.

Eiji's life takes a dramatic turn when he is targeted by other Order Users, including his childhood friend Rin Kurenai, who seeks to control his power for her own agenda. Rin, a powerful Order User herself, leads an organization called Big Order, which aims to reshape the world according to her vision. As Eiji becomes entangled in the conflict between Order Users, he must confront his own desires and the moral implications of his abilities. Along the way, he encounters a diverse cast of characters, each with their own motivations and Orders, including Sena Hoshimiya, Eiji's younger sister, who possesses her own unique powers.

The narrative explores themes of power, responsibility, and the consequences of one's actions as Eiji struggles to protect those he cares about while grappling with the destructive potential of his Order. The series blends action, drama, and psychological elements, with a focus on the moral dilemmas faced by its characters. The plot unfolds through a series of confrontations and alliances, culminating in a climactic battle that determines the fate of the world. "Big Order" presents a complex and often chaotic story, with twists and revelations that challenge the characters' perceptions of right and wrong.