Luigi is Mario's younger twin brother in the 1986 Japanese anime film. The brothers live together and run a grocery store where Luigi works. Physically, Luigi stands taller than Mario and wears blue overalls over a yellow shirt, plus a blue hat marked with a yellow "L".

Initially skeptical, Luigi dismisses Mario's story of Princess Peach emerging from their television as a dream and goes back to sleep. The next day, discovering Peach's discarded emerald pendant changes his mind. He identifies it as a legendary Mushroom Kingdom artifact capable of guiding its holder to that realm, referencing Toad folklore about its link to untold riches. This realization prompts him to join the rescue mission.

During the journey, Luigi complains frequently about hunger, even briefly contemplating roasting their canine companion Kibidango. His susceptibility to temptation surfaces when, distracted by hunger, he follows two Goombas into a valley filled with hallucinogenic mushrooms. Consuming them triggers alternating fits of hysterical laughter and tears, requiring Mario to administer more mushrooms to counter the effects.

Luigi shows a pragmatic focus on material rewards, asking Kinoko Sennin about potential payment upon hearing of Bowser's conquest. The sage points to the kingdom's abundant gold coins. This advice shapes Luigi's actions: he immediately collects coins transformed from rescued Toads and later follows a coin trail into a Goomba trap within a gold mine.

Throughout the quest, Luigi functions primarily in a supporting role to Mario. He accompanies Mario through pipes transporting them to the Mushroom Kingdom, follows Kinoko Sennin's directive to travel east toward Bowser's stronghold, and stays with the group facing environmental hazards and enemies like Piranha Plants and Lakitu. His participation remains consistent but secondary to Mario's leadership in the mission to rescue Princess Peach.