As the thirteenth generation descendant of the legendary outlaw Ishikawa Goemon, this character carries the weight of a storied lineage as a renegade samurai. Initially conceived by creator Monkey Punch as a traditionally Japanese counterpoint to the otherwise international cast, his very design was inspired by the master swordsman Kyuzo from Akira Kurosawa's Seven Samurai. In the narrative of The Mystery of Mamo, Goemon Ishikawa XIII exists as the stoic and immensely skilled sword master of Lupin's gang, a figure of fierce loyalty and profound personal honor whose primary tool is the legendary Zantetsuken, a blade capable of slicing through virtually any physical material, including steel and bullets.

In terms of personality, Goemon is defined by a deep-seated pride in his abilities, which is matched only by the extreme shame he feels upon any form of failure. A pivotal moment demonstrating this occurs in The Mystery of Mamo, where his unbreakable sword, the Zantetsuken, is shattered in a battle against the brute Flinch, an event that causes him significant dishonor and remorse. He carries himself with a quiet, mellow aloofness and maintains a strict adherence to Japanese traditions, favoring a diet of Japanese cuisine, wearing traditional kimono and hakama, and practicing Buddhism and Shinto. He is often seen meditating, and his signature phrase, uttered after cutting down an enemy's weapon or vehicle rather than a person, is the solemn declaration that he has once again cut a worthless object. Despite his lethal precision, he refrains from taking human life unless formally challenged to a duel.

Regarding his role in the story and key relationships, Goemon operates as a member of Arsene Lupin III's gang, though his participation is less frequent than that of Daisuke Jigen. His relationship with Lupin is complex; while he has developed a genuine loyalty and will protect his comrades, he is easily annoyed by Lupin's reckless and lecherous antics, particularly his infatuation with Fujiko Mine. In The Mystery of Mamo, his motivations are notably pragmatic, as he claims to help Lupin primarily to ensure he can keep his own vow to be the one who eventually delivers the thief his deathblow. He shares a much more amicable and respectful bond with Jigen, viewing him as a fellow honorable warrior and reliable partner during operations. His relationship with Fujiko is strained due to her constant betrayals; his distrust is so apparent that when she arrives in the film, his reaction is one of visible exasperation.

The character also undergoes notable development and possesses a distinct set of abilities. While his past in the original manga involved being a dangerous enemy of Lupin, by the time of the film, he is a trusted, if sometimes reluctant, ally. His backstory includes training under an Iga ninja master, which explains his proficiency in espionage and justifies his acceptance of thievery despite his samurai ethics. His martial prowess extends far beyond swordsmanship to include disciplines such as kenjutsu, battōjutsu, jujutsu, aikido, and karate, allowing him to defeat multiple unarmed opponents with ease. However, he also has notable vulnerabilities, including a surprising weakness for scams promising enlightenment, a deep naivete regarding seemingly innocent women, and an inability to handle overt female sexuality, which renders him uncomfortable and immobilized. The breaking of his Zantetsuken in The Mystery of Mamo serves as a critical test of his character, forcing him to confront failure and ultimately continue fighting using his unarmed skills.