Baby Ramu, an infant thrust into Lupin and Jigen's custody during a heist under ambiguous circumstances, becomes their temporary ward. His distinctive appearance is frequently noted as atypically unattractive for an animated baby. Ramu's digestive issues trigger a prolonged gastrointestinal episode, later revealing he swallowed a crucial gem at the narrative's climax—its recovery pivots on this excretion.

His presence forges unexpected bonds: Jigen forms a reluctant caretaking partnership, while Goemon misinterprets the situation initially but later gifts him a traditional Japanese toy, showing attachment. Ramu connects the thieves to sky pirate Yutika and royal guards Jiva and Camilla, who display protective instincts toward him.

Functioning as both comic relief through bodily humor and an accidental plot device via the ingested treasure, Ramu complicates the thieves' action sequences with safety concerns. Though merely a royal guard's child from Shahalta, his role surpasses this ordinary origin. He primarily drives unconventional teamwork dynamics, forcing Lupin and Jigen to navigate heists alongside infant care duties.