Poseidon’s role in EPIC: The Musical begins after Odysseus blinds Polyphemus, his son, during The Ocean Saga. Enraged by the attack, Poseidon summons a massive storm that blocks Odysseus’ route to Ithaca and causes the destruction of most of his fleet. He later confronts Odysseus after the crew opens Aeolus’ bag of wind. Here, Poseidon ridicules him for being weak and too merciful, delivering a brutal beatdown using his hydrokinesis to whip up towering waves and tempests. With only one ship left, Odysseus narrowly escapes using the winds. Poseidon’s godly presence is marked by the musical theme “Ruthlessness,” where his abilities dominate both the stage and the soundscape.

After several years of silence, Poseidon returns with terrifying power in The Vengeance Saga. As Odysseus nears Ithaca, Poseidon ambushes him and threatens to flood the entire kingdom unless the hero sacrifices himself. He even vows to gouge out Telemachus' eyes in revenge for Polyphemus. A fierce battle follows, and Poseidon hurls his ultimate move, Shatter the Ocean, a devastating attack in which he conjures a massive image of himself and smashes the sea as if it were glass. Despite the onslaught, Odysseus survives by using Hermes’ wind bag, eventually gaining the upper hand. The musical score reflects Poseidon's rage growing out of control, with increasingly distorted and electrified brass sounds underscoring the chaos.

Although immortal, Poseidon is physically overpowered and psychologically tormented by Odysseus, who uses his remaining strength and cunning to force the sea god to surrender and call off the storm. Poseidon, weakened and humiliated, retreats with a final bitter remark about how far Odysseus has fallen. His powers—hydrokinesis, Laestrygonian summoning, and his world-shattering trident attack—cement him as one of the most overwhelming forces in the musical. Even in defeat, Poseidon remains a haunting presence, symbolic of divine wrath and the price of vengeance carried too far.