Bushido is a warrior code that originated in medieval Japan and was adopted by the Draconis Combine as a moral compass for their military forces. It values honor, loyalty to one's commander, and duty unto death.
The code was likely originally developed in the 11th through 14th centuries in Japan. In the Tokugawa Shogunate the code was formalized as a feudal law. Elements of the code, including the concept of face and especially that of honor strongly influenced most Japanese dealings with one another and with the rest of Terra. It later became the code of conduct for the Draconis Combine Mustered Soldiery.
Bushido provides a moral compass for its adherents and stresses frugality, loyalty, mastery of the martial arts, and honor unto death. There are seven virtues for the code:
In addition to these tenets was a reverence of the katana, or sword of the samurai. Many members of the DCMS carry katana with them into battle, even in their BattleMech cockpits. The daisho, or twinned-blades, consists of a katana and a wakizashi and are normally only possessed by individuals with long and distinguished lineages, sometimes dating back to feudal Japan. Many katana and daisho were named by their owners and those names carried on with descendants. The daisho were permitted to be worn only by samurai; anyone other than a samurai could be executed for doing so.
Ronin are masterless samurai but many were still adherents to bushido. While they no longer served a lord, they still upheld the same beliefs they had before. Until the mid-17th century, ronin were generally perceived as outcasts, but two events changed the belief.
The first was the exceptional life of Miyamoto Musashi changed many of those. Musashi, a skilled swordsman, traveled extensively around Japan and joined those causes about which he felt a connection. Musashi later wrote a book called the Go Rin No Sho (or "Book of Five Rings") that codified his tactics. Unusually, Musashi also used two katana, rather than a daisho in his battles. In one of his most famous duels he killed Sasaki Kojiro by using a bokken, or wooden sword, matched against Kojiro's nodachi, or long sword. Musashi was believed never to have lost one of the more than sixty duels in which he participated.
The other was the story of the Forty-Seven Ronin  from the 18th century that served to change the perceptions of ronin. These samurai were left without a master when their daimyo (lord) was forced to commit seppuku after assaulting a court official. The forty-seven ronin plotted for a year to assassinate the official knowing that they would be forced to commit seppuku as well if successful. The ronin's plan to quell the fear of the official worked and after a year, he let down his guard. At that moment the forty-seven ronin attacked and beheaded the official, bearing his head back to the tomb of their daimyo. While the ronin had acted within the precepts of bushido, they had violated the edict of the Shogun and, rather than having them executed, he ordered them to commit seppuku. Forty-six of the group did so and were entombed. The forty-seventh had been sent away to inform the family of the daimyos of the action and when he returned, he was pardoned by the Shogun. When he died, he was entombed with his forty-six brethren.
In the Draconis Combine, the traditional beliefs about ronin persist. Mercenaries, in particular, are viewed as worse than ronin as they hire out their services. Many in the Combine's military believe that mercenaries are without honor and treat them as such. Rarely are mercenaries treated well, with the notable exceptions of Wolf's Dragoons and the interactions between Morgan Kell and Yorinaga Kurita.