"Mojako" centers around a young boy named Mojako, who discovers a mysterious, ancient artifact in his grandfather's attic. This artifact, known as the "Eclipse Orb," grants him the ability to summon and control powerful elemental spirits. However, the orb also attracts the attention of a secretive organization called the Obsidian Order, which seeks to harness its power for their own nefarious purposes. As Mojako learns to master the orb's abilities, he is joined by a group of allies, each with their own unique skills and motivations, including Lina, a skilled martial artist, and Taro, a tech-savvy inventor.

The narrative unfolds as Mojako and his friends embark on a journey to protect the orb from falling into the wrong hands. Along the way, they encounter various challenges, including battles with the Obsidian Order's elite enforcers and the discovery of other ancient artifacts with similar powers. The story delves into themes of friendship, responsibility, and the consequences of wielding great power. As the group travels across diverse landscapes, from bustling cities to remote wilderness, they uncover the orb's true origins and its connection to a long-forgotten civilization.

The main characters are developed through their interactions and growth over the course of the series. Mojako evolves from a naive and uncertain boy into a determined leader, while Lina and Taro provide both physical and intellectual support, each contributing to the group's success in their own way. The Obsidian Order's enigmatic leader, known only as "The Shadow," serves as the primary antagonist, with a complex backstory that gradually reveals their motivations and ties to the orb.

The plot is driven by a series of escalating conflicts, culminating in a final confrontation where Mojako must make a critical decision about the orb's fate. The series balances action-packed sequences with moments of introspection, exploring the moral dilemmas faced by the characters as they navigate their roles in a world where power and responsibility are inextricably linked.