Goemon Ishikawa XIII, the thirteenth-generation descendant of the historical figure Ishikawa Goemon, upholds his legacy as a master swordsman and thief. His signature weapon is the Zantetsuken sword, capable of slicing through nearly any material—steel, bullets, even buildings. Despite this destructive power, he frequently employs it non-lethally, disarming opponents by destroying their weapons and clothing, then uttering his characteristic phrase: "I have cut yet another worthless object." This reflects his conviction that a katana should draw blood before being sheathed. His martial prowess extends beyond swordsmanship to encompass Jujutsu, Aikido, and Karate, enabling him to overcome multiple attackers unarmed.

He adheres strictly to traditional Japanese customs, wearing hakama and fundoshi, consuming only Japanese cuisine, and observing Buddhist and Shinto rituals. His disciplined daily routines emphasize meditation, maintained even under duress, alongside activities like fishing, noh theater, and martial arts competitions. Typically stoic and aloof, he exhibits occasional flashes of frustration or humor, especially around women. He displays pronounced shyness toward attractive women, often blushing or averting his gaze, and remains easily misled by those appearing innocent or trustworthy—a vulnerability that frequently leads to complications, contrasting his otherwise rigid discipline.

Within group dynamics, he operates as a key associate of Arsène Lupin III, though his involvement hinges on personal interest. His loyalty evolved from initial antagonism, marked by repeated assassination attempts on Lupin, into a steadfast partnership forged when Lupin aided his quest for vengeance. He shares respectful camaraderie with Daisuke Jigen, viewing him as a fellow warrior, but distrusts Fujiko Mine due to her manipulative nature, despite occasionally assisting her. He frequently challenges Lupin's frivolous behavior, particularly concerning women or morally dubious schemes, and has vowed to deliver Lupin's deathblow as their final shared act. Intense shame grips him when he fails a task or his sword is damaged or misused, prompting periods of solitary training or meditation.

In *Blood Seal of the Eternal Mermaid*, he joins the pursuit of the "Mermaid's Scale" gem and its link to immortality. His role involves deploying the Zantetsuken against enhanced adversaries like the antagonist Himuro, who transforms into a monstrous entity after consuming immortal blood. Goemon's decisive intervention, alongside Jigen, proves critical in neutralizing Himuro through decapitation and incineration, showcasing his adaptability against supernatural threats. These actions align with his ethical code, reserving lethal force solely for irredeemable foes.

His background includes ninja training under Momochi no Jijii, explaining his acceptance of theft despite samurai heritage. He struggles with financial naivete, falling for scams promising enlightenment, and charges Lupin for services to offset these losses. Across all media, he embodies a blend of unwavering discipline, cultural devotion, and situational vulnerability, maintaining consistent principles while adapting to varied narrative contexts.