Monkey D. Luffy's actions in *One Piece 3D: Mugiwara Chase* stem from his deep attachment to his straw hat, a symbol of his promise to Shanks. After a bird steals the hat, Luffy reacts with distress, frantically searching and nearly drowning, underscoring its irreplaceable value to his identity. He rallies his entire crew, the Straw Hat Pirates, demonstrating his leadership and their loyalty as they pursue the thief. They split into teams using specialized vehicles like the Shark Submerge III and Mini Merry II, chasing across treacherous glaciers, through Marine blockades, inside caves, over waterfalls, and into Sea King-infested waters.

Luffy employs his rubber Devil Fruit powers to overcome obstacles and confront the bird directly, persisting despite Marine forces and giant adversaries. The bird is revealed as Buzz, a dog who consumed the Tori Tori no Mi, Model: Eagle Devil Fruit. Buzz stole the hat at the request of his owner, Schneider, who mistakenly believed he was dying and wanted to spare Buzz. Learning this, Luffy moves from confrontation to understanding. He becomes enraged when a Marine officer damages the hat but stays focused on recovery. Luffy ultimately retrieves the hat with Buzz's help after a flood engulfs the Marine base, prioritizing the hat's safety over retaliation.

The resolution highlights Luffy's empathy. Once Schneider explains Buzz's motive and Chopper reveals Schneider's illness resulted from an accidentally swallowed fork—not a fatal condition—Luffy bears no grudge against Buzz or Schneider. The crew returns them to their ship peacefully, with Schneider advising Luffy to protect the hat. This reinforces Luffy's core nature: fiercely protective of his symbolic treasure, yet responding to sincere intentions with compassion instead of vengeance.