"Porco Rosso" is set in the Adriatic Sea during the interwar period of the 1920s and 1930s, a time when air pirates and bounty hunters dominate the skies. The protagonist, Marco Pagot, is a former World War I flying ace who has been mysteriously transformed into a pig, earning him the nickname Porco Rosso, or "Crimson Pig." He now works as a freelance bounty hunter, protecting ships from airborne bandits. Despite his porcine appearance, Porco retains his human intellect, piloting skills, and a deep sense of honor.

The narrative begins with Porco intercepting a group of air pirates led by the flamboyant Mamma Aiuto Gang, who are harassing a cruise ship. After thwarting their plans, Porco becomes a target for the pirates, who hire the arrogant American pilot Donald Curtis to eliminate him. Curtis, a self-proclaimed ace and Hollywood star, challenges Porco to a duel, leading to a dogfight that ends with Porco's plane being severely damaged. Forced to retreat, Porco seeks repairs at the workshop of his old friend, Madame Gina, who runs a secluded hotel on an island. Gina harbors unspoken feelings for Porco, but he remains emotionally distant, haunted by his past and the curse that transformed him.

To restore his plane, Porco travels to Milan, where he enlists the help of the skilled but inexperienced aircraft mechanic Fio Piccolo. Despite initial skepticism about her abilities due to her youth and gender, Fio proves her talent and determination, earning Porco's respect. Together, they rebuild his plane, incorporating innovative designs that give it an edge in combat. Meanwhile, Curtis continues to pursue Porco, driven by a mix of professional rivalry and personal ambition.

The story culminates in a climactic rematch between Porco and Curtis, set against the backdrop of a grand aerial duel witnessed by Gina, Fio, and the air pirates. The battle is intense and showcases Porco's ingenuity and experience as a pilot. The outcome of the duel is left somewhat ambiguous, with the focus shifting to Porco's internal struggle and his unresolved feelings about his past, his curse, and his relationships with Gina and Fio. The film concludes on an open-ended note, emphasizing themes of redemption, identity, and the enduring allure of the skies.

Throughout the narrative, "Porco Rosso" explores themes of honor, nostalgia, and the impact of war, all while maintaining a balance between action, humor, and introspection. The characters are richly developed, with Porco's enigmatic personality and moral complexity standing at the center of the story. The film's setting and period details provide a vivid backdrop, immersing viewers in a world where aviation and adventure intersect with personal and historical legacies.