Goemon has a much more amicable relationship with Jigen. Goemon sees Jigen as a fellow honorable warrior, while Jigen sees Goemon as a trustworthy "foxhole buddy," and the two are frequently paired together during jobs, and usually help keep Lupin in check.
On the odd occasion and increasingly in recent years, Goemon will ally himself with Fujiko, in spite of his distrust of her. As long as their goal is the same and Fujiko makes no attempts to betray him, the two work well together and usually achieve what they seek.
In the manga, Goemon first appears as a very dangerous enemy of Lupin. Lupin attempts to steal Goemon's master's alchemic formula through infiltration of Goemon's clan, but his cover is blown by Fujiko, who happens to be Goemon's girlfriend at the time. Goemon makes many attempts to kill Lupin over the next several volumes, making attempts ranging from hiring assassins as skilled as Jigen himself to entering the service of three martial masters to planting bombs in Lupin's belongings. Eventually, however, he is convinced that he could learn much more working for Lupin than against him, and rather abruptly switches his allegiance. His position at Lupin's side is cemented when Lupin ruins the government's case against the man who killed Goemon's uncle, allowing Goemon to take his revenge as brutally and publicly as he wants without having to break in to prison to do so.
By the events of the second manga series, Lupin trusts Goemon implicitly, and Goemon reciprocates. When a rival of Lupin captures and hideously tortures Goemon, Goemon refuses to even respond to his interrogation except to say that Lupin would find him and allow him to take revenge. Lupin then captures and seduces his rival's wife, and uses the information gleaned thereof to release Goemon, who slays his captor with Jigen's help.
In Dragon of Doom, Kikyo was once a childhood friend of Goemon. When she returned to aid Goemon, she was all grown-up. She eventually became his love interest in the movie and traveled together to get the small dragon figurine which Lupin found from what's left of the Titanic. Later, Kikyo faked her death so she could turn on Goemon, steal the dragon figurine and side with Chin Chin Chao. Kikyo helped Chao to uncover the secret of the dragon figurine, and used its alloy to make an unstoppable stealth fighter. However, Goemon used his sword and skills to slice the fighter three times at the same spot. It was destroyed and Kikyo fell into the very same spot the Titanic sink, resting with her grandfather who stole the dragon figurine in the first place.
Sadachiyo the Scorpion appears in Secret of the Twilight Gemini. He was a highly-trained assassin who was hired by a rogue faction within the Geltic tribe. Causing problems for both Lupin and Goemon throughout the special, Sadachiyo dueled Goemon to the death in the end. Sadachiyo's sword broke the tip of Goemon's Zantetsuken, only for the tip to land in Sadachiyo's back and pierce his heart.
In The Fuma Conspiracy, Goemon nearly marries into the Suminawa clan by marrying Murasaki Suminawa, the daughter of one of his instructors. The engagement eventually falls through, though Goemon and Murasaki part on friendly terms.
Goemon's most oft-seen pastime is meditation; during inactive moments, even with potential danger near, he is usually seated on the floor with legs crossed, eyes closed. Like most of the Lupin gang he is a trained driver and pilot, although he prefers being a passenger rather than taking the driver seat.
Goemon shows allegiance to Japanese culture as strictly as his travelling and unique lifestyle can allow. He dresses in an hakama and wears fundoshi instead of underwear. His preferred food is Japanese cuisine. Although he may toast with champagne, his drink of choice is sake. In unoccasional moments, he has been seen smoking a traditional bamboo kiseru. His favorite music is enka, or as Jigen calls it, "elevator music".
Although his demeanor is stoically mellow, Goemon has been seen exploding with frustration, admiring beautiful women, and...very rarely...screaming in fright. Such lapses of discipline are usually treated as humorous takes. His martial arts training gives him many extraordinary skills, i.e., underwater breath control for diving without an aqualung and a limited understanding of the supernatural. He can easily best several trained thugs in unarmed combat and can barehandedly catch an arrow or thrown dagger. His trademark talent is sword slicing bullets mid-flight before they make contact. It should be mentioned that, despite the deadliness of his weapon, Goemon will never take a human life unless challenged to a duel, and even then only if the opponent reveals a dishonorable nature.
If Goemon has a true weakness, it is that he's even more weak with women than Lupin is. He readily trusts any woman who seems superficially trustworthy or innocent, often landing him in much trouble. At the same time, he fears sultry women will distract him from his training, and tends to blush or flee when any woman is put in less than modest situation.
Goemon also is very bad with money, and constantly charges Lupin for his services in some fashion. What he does with the money is a usually complete mystery. In $1 Money Wars he gives it to the female leader of a cult, who promptly runs off with it.
Commonly thought to be just a samurai, an episode of Shin Lupin III, ("Goemon's Revenge") has Goemon visiting his Iga Ninja sensei. This episode depicts him as having had the training of a master ninja, perhaps giving some reason behind his willingness to find thievery as an acceptable practice, in spite of his samurai ways.
In the original manga, Goemon is targeted by Lupin to steal the secrets of how to make his sword, or in the American release, how to make gold. In later issues, Goemon is sent by his masters to kill Lupin, but after failing many times, he decides Lupin can teach him more and joins his side.
In episode five of the first anime series, Goemon is tricked into going against Lupin by Old Man Momochi, who wants them both out of the way so he can claim the title of world's greatest assassin. The two both outwit him and survive. Two episodes later, Lupin attempts to steal the sword formula; after being outsmarted, Goemon gets revenge by slicing Lupin's car in half. After both break down into homeric laughter over the situation, Goemon decides to join the gang. The two episodes pull in several elements from the manga stories.
In the 2002 TV special "First Contact", Goemon met Lupin when he was searching for the Zantetsuken, the only sword he felt worthy of his abilities. Lupin, Jigen, and Fujiko all served as adversaries until being forced to work together to survive. There are hints that parts of the story may be made up at the end of the special, however, so not everything can be taken as true.
Zantetsuken has had a number of origin stories over the years, including having been made from the metal of a fallen meteor, or made from a special alloy passed down through Goemon's clan. In his first TV appearance, the sword is described as being forged from three famous or mystical Japanese swords. A common explanation for its existence is still argued, but its strength and sharpness are constants in every Lupin III incarnation. However, Zantetsuken has also been known to chip or break when applied to a particularly tenacious surface; usually its failure indicates circumstances are the worst possible for Goemon and the rest of Lupin's gang. It is unknown how Goemon has the blade repaired after such damage. It is revealed in Shin Lupin III that Zantetsuken has at least one known weakness; it cannot cut konnyaku gel.
The second series also gives Zantetsuken a more mystical ability; on a few occasions, the blade acquires a shadow, showing death lurks nearby for Lupin and his gang. Likewise, when the shadow disappears, it shows that the danger has passed. This trait of Zantetsuken appears to be unique to Shin Lupin III, however, and has never been used in any version of Lupin III afterwards.
Zantetsuken is also the source of Goemon's most famous catchphrase, "Once again I have cut a worthless object," which he says whenever he uses Zantetsuken to do something spectacular that he nonetheless considers mundane (for instance, cutting down a helicopter chasing his friends in Secret of Mamo). This has been referenced many times in other anime and manga, and has become something of a joke within Lupin itself. In Da Capo of Love: Fujiko's Unlucky Days, Lupin even tells Goemon, "No one is better at cutting worthless objects than you!"