1. His Origin Is Basically "Batman on Steroids"
There are more retellings of the story of Ishikawa Goemon (1558 – 1594) than the number of dick diseases the Merry Men collectively must have had, though most are about as bloody. In most versions, Goemon was born to a high-ish ranking samurai family and lost his parents at 15 when they fell out of favor with the ruling government and were killed. Fleeing his home, he sought to learn the art of ninjutsu from legendary ninja master Sandayu Momochi. His training was apparently going well until, that is, he started practicing the art of disappearing his penis inside Sandayu's mistress' vagina. It's actually kind of refreshing that even in the midst of a revenge-fueled superhero training, Goemon still found the time to take a break and relax. It's called self-care, sweeties.
Unfortunately, his master did not see it that way and expelled Goemon, who also stole Sandayu's prized sword on his way out. And judging by how Goemon is depicted in most media, he probably took the sword off the wall in plain view of his master and walked out the door while maintaining eye contact with him. See, although Goemon is sometimes described as a sleek ninja figure, most sources portray him as an absolute unit, a towering, hulking giant with an afro to boot. We're just going to assume that there's already an anime out there where Goemon pulls out various ninja implements like shuriken etc. out of his hairdo. There just has to be. Anyway, after going freelance, Goemon started robbing the rich and giving to the poor, but it's the way he did it that's made him a total legend.
2. Ishikawa Goemon Straight Up Had Magic Powers
Robin Hood's legend is about 700 years old, and in all that time, the most the character ever did was become a slightly worse version of Hawkeye. Now let's look at Japan.
History is like 95% sure that Ishikawa Goemon was a real person but, being the massive nerd that it is, history also reminds everyone that, at most, Goemon was a leader of a group of thieves and burglars who may have once or twice thrown money behind them as a distraction while running from the authorities. This most likely evolved over time into the legend of a noble outlaw who shared the spoils of his thieving with the peasants, instead of the much more realistic version of him and his men spending it all at local brothels. But screw reality. Reality blows. Reality killed all of our childhood dogs instead of letting them live on that nice farm upstate. Which is why Japan decided not to be burdened with reality when building up the legend of Ishikawa Goemon.
First of all, he can fly. Yup. He can just float in the air on a cloud of his own awesomeness. It's how he was able to get into so many well-guarded rich-guy mansions. What else? Oh, nothing, just little things like being able to teleport magically from one place to another in a puff of smoke (remember, ninja). Then again, why would he need to teleport when he could also turn invisible? Edo (old-timey Tokyo) probably started the whole magic bit, attributing nearly every crime committed against the rich and powerful to Goemon. Essentially, whenever someone who never had sleep for dinner as much as slipped in their own homes, the authorities would immediately charge Goemon with aggravated secret floor waxing. With time, that really revved up people's imagination, and they started immortalizing Goemon's superhuman exploits in stage plays, etc. Well, actually, what really got them going was how Goemon died.