Wild and outgoing, Mugen is a wandering swordsman from Ryukyu (islands to the south of Japan) that has vowed to defeat anyone who
gets in his way. He has had a little problem with that vow, seeing as he cannot seem to defeat the mysterious swordsman Jin. Thanks to a deal with Fuu, he has traveled with Jin for some time.
After fighting Jin in a bar and being captured by authorities for chopping off the arm of the governor's son, they start to recall what got them in the situation they're in in the first place.
Mugen utilizes highly unorthodox swordplay and a fighting style based on breakdancing and resembling capoeira - dubbed "champuru kendo," ostensibly developed by himself - taking bits and pieces from all forms of martial arts and making up the rest as he fights his opponents, make him a force to be reckoned with. An example of this being his battle with Shouryuu, as he was able to mimic and use the technique 'Hakkei' seemingly picked up in their first duel, turning the tide of the battle. His fighting style is best summarized by Kariya Kagetoki during their fight in Episode 25: "Interesting. You utilize erratic movements to prevent anyone from predicting them. But you fail to utilize your martial arts skills. By relying only on reflex and instinct, you inadvertently show the limitations of your skills to your opponent." Later in the series he had a small control of "chi", in which he learned from his opponent at the time. In the end he was able to kill is opponent and win the match. ( only used once in the series)
His limitations were further exploited in his fight with Denkibou while on a small boat, as his inability to fight well in small areas was shown. This is further evident in that his moves become increasingly erratic and unique as his opponents are more powerful. He carries two blades; his principal weapon a unique sword with a curved blade and a hilt with two prongs sheathed across his back and the other a small tanto concealed at the end of his scabbard (only resorted to as a trump card). His main weapon appears to be an amalgamation of the Okinawan sai and Japanese katana. Mugen also has a tendency to parry attacks with the steel base of his geta. His clothing is anachronistic as well, reminiscent of baggy hip-hop fashions of today: his gi functions more like a jacket and his hakama is cut off at shorts-length, resembling loose-fitting Bermuda shorts. His black hair is unkempt and similar to an afro or Spike Spiegel's hair from Cowboy Bebop.
Mugen seems to be incapable of dying, or at the very least has a body that is more resistant to life-threatening injuries than the average person. When on the verge of death, he appears to cross into a mystical world in the Ryūkyūan religion called Nirai Kanai—depicted in Samurai Champloo as an upside-down mirror world—overseen by the Futuchi who are dressed in black-feathered robes and carry spears. With each visit to this world he is subsequently 'rejected.' He has been brought back to life in this manner on at least three occasions. It has been speculated that his survival is because he is being preserved for a greater purpose.