"Arifureta - From Commonplace to World's Strongest: Zero" serves as a prequel to the main "Arifureta" series, delving into the origins of the Liberators and the ancient world before Hajime Nagumo's arrival. The story centers on Oscar Orcus, a brilliant but frail alchemist, and Miledi Reisen, a cheerful yet determined young woman who becomes the leader of the Liberators. Set in a world where humanity is oppressed by the gods and their apostles, the narrative explores the formation of the Liberators, a group dedicated to overthrowing divine tyranny and freeing humanity.

Oscar, initially a reclusive scholar, is drawn into the conflict when Miledi recruits him to join her cause. Despite his reluctance, Oscar's unparalleled knowledge of ancient magic and alchemy makes him a valuable asset. Miledi, driven by a desire to protect the weak and challenge the gods, inspires others to join their rebellion. Together, they gather allies, including Naiz Gruen, a stoic warrior, and Lyutillis, a powerful mage, forming the core of the Liberators.

The plot follows their efforts to uncover ancient ruins, develop powerful artifacts, and rally humanity against the gods. Oscar's inventions, such as the concept of transmutation and the creation of powerful weapons, play a pivotal role in their struggle. The group faces numerous challenges, including betrayal, internal conflicts, and the overwhelming power of the gods' apostles. As the Liberators grow in strength, they must confront the moral complexities of their mission and the sacrifices required to achieve their goals.

The manga explores themes of resilience, camaraderie, and the fight against oppression, while providing deeper context for the world and events of the main series. Through its focus on Oscar and Miledi, it offers insight into the origins of the Liberators' ideals and the legacy they leave behind, setting the stage for the events of "Arifureta - From Commonplace to World's Strongest."