"Alexander's Decision" is a historical fantasy anime series that reimagines the life and conquests of Alexander the Great, blending historical events with supernatural elements. The narrative begins with Alexander as a young prince in Macedon, grappling with the weight of his destiny and the expectations placed upon him by his father, King Philip II. A pivotal moment occurs when Alexander encounters a mysterious oracle who reveals that his fate is intertwined with ancient, otherworldly forces. This revelation sets him on a path to not only conquer the known world but also to uncover the truth behind his divine lineage.

As Alexander ascends to the throne after his father's assassination, he embarks on a campaign to expand his empire, driven by a vision of uniting the world under a single banner. The series meticulously portrays his military strategies, alliances, and battles, including the iconic sieges of Tyre and Gaugamela. However, the story diverges from historical accounts by introducing supernatural adversaries and mythical creatures that challenge Alexander and his army. These elements are woven into the narrative as manifestations of the ancient forces the oracle spoke of, testing Alexander's resolve and leadership.

Key characters include Hephaestion, Alexander's closest companion and confidant, whose loyalty and strategic mind prove invaluable; Roxana, a Persian noblewoman whose relationship with Alexander adds complexity to his character; and Ptolemy, a general whose pragmatism often contrasts with Alexander's idealism. The series also introduces original characters, such as a enigmatic sorceress who aids Alexander in his quest, and a rival warlord empowered by the same ancient forces, creating a dynamic interplay between historical and fantastical elements.

The plot explores themes of ambition, destiny, and the cost of power, as Alexander's relentless pursuit of conquest begins to take a toll on his relationships and his own psyche. The supernatural elements escalate as he nears the edges of the known world, culminating in a climactic confrontation with the source of the ancient forces. The series concludes with Alexander's legacy left ambiguous, blending historical ambiguity with the fantastical elements introduced throughout the story.