Gian dominates his neighborhood with his imposing size and aggressive bullying, routinely seizing toys and manga from others—especially Nobita—under the thin guise of "borrowing." Yet this intimidating figure harbors fierce loyalty toward his younger sister Jaiko, actively supporting her comic book creations, occasionally with gadgets taken from peers. His bravado instantly crumbles before his mother, the local grocery store owner; her mere presence sends him fleeing when he’s caught misbehaving or neglecting duties.

Blindly overconfident, Gian believes himself a gifted singer and chef, subjecting others to his grating voice and disastrous cooking without recognizing their flaws. He founded and captains the baseball team "The Giants," where losses—frequently tied to Nobita’s athletic struggles—ignite his fury, driving him to lash out at teammates over his win-at-all-costs mentality.

His bonds twist unpredictably: Suneo serves as both accomplice and victim, manipulated for resources despite their friendship. While often tormenting Nobita, Gian sporadically unveils buried concern, rescuing him from peril or offering aid during illness. Fleeting introspection, like realizing his unpopularity at a birthday, sparks shallow self-improvement urges, though peers like Suneo swiftly derail them. Gian typically halts his aggression when Shizuka intervenes, respecting her despite one attempted retaliation.

He claims affection for his dog Muku, though he neglects its care and openly mocks it. Rare compassionate flashes emerge—collaborating to save animals or offering genuine sympathy—but they drown in his habitual selfishness and cruelty. His philosophy, "What’s yours is mine and what’s mine is mine," crystallizes his possessive, domineering worldview.