Mario operates "Marriott Lunch Market," a selective used clothing shop specializing in vintage and curated fashion items. He is first encountered when Kakushi Gotou visits during his commute. Mario collaborates closely with Kakushi, helping preserve the secret of his manga artist career from his daughter. He stores Kakushi's work attire at the shop, allowing Kakushi to change out of his salaryman disguise upon arrival, and often refers to him as "Clark Kent" due to this dual identity.

Mario extends logistical support beyond clothing services. He personally attends Kakushi's autograph sessions to maintain secrecy and provides him with a vehicle bearing the shop's logo for transportation. On one occasion, Mario accidentally sold Kakushi's entire suit, an event which unintentionally sparked a new fashion style.

His involvement deepens in significant personal events for the Gotou family. Initially appearing infrequently in the manga's middle sections, the character demonstrated greater narrative potential in animation. Mario consequently reappeared in crucial later scenes, including Hime Gotou's birthday celebration and the series' concluding episodes.

Mario exhibits a flamboyant personality, though specific behavioral details are not elaborated. Kakushi observes that the shop reportedly experiences low customer traffic. Mario's real name remains undisclosed throughout the series.