You just admitted you don't believe there is one and even if I showed you things related to it you'd just deny them because of your perception.
Zoro has a nickname. It's "Mr. Bushido."
Zoro went to Isshin Dojo (a Kenjutsu school) as a child and that's where he learned the Japanese swordsmanship art of the samurai along with it.
Bushido is the code of conduct for the samurai class in premodern Japan, and kenjutsu is the swordsmanship that samurai were trained in:
Bushido
The code of conduct for the samurai, or bushi (warrior), class of premodern Japan. Bushido is rooted in Buddhist and Confucian philosophies, and emphasizes virtues such as honor, integrity, self-mastery, justice, courage, benevolence, politeness, and self-control.
Kenjutsu
The swordsmanship that samurai were trained in. Kenjutsu is imbued with a rich philosophical and spiritual tradition, and practitioners emphasize principles such as honor, integrity, and self-mastery. The exact activities and conventions undertaken when practicing kenjutsu vary from school to school.
This should help to clarify what a swordsman's code of honor is and how it applies in the story. Certainly not everybody uses the same kind Zoro does, and some swordsmen have no code of conduct at all, but the actual idea behind this is that there are forms of innate knowledge associated with these things.
"He's a stinkin' aggressive
pirate swordsman who practices the Three-Sword Style."
I just thought this would be supportive to post for those who were arguing about whether Zoro can be considered a pirate or a swordsman. He's both.
Bushido guys tend to have a habit of announcing their names before they fight and stuff like that for honor. They encourage admitting defeat gracefully to maintain integrity, too. It's not good form to be sour after a duel. Mihawk had recognized qualities in Zoro that stem from Bushido and deemed him a strong person because of it. Though, I think that just means he identifies a strong will with a strong sense of moral principles or something.
If there is a style of swordsmanship, then it has usually been learned somewhere and that place will often have a code of conduct paired with it in the same way Bushido and Kenjutsu are paired. Mihawk has his own sense of it. The issue with him concerning this is that we don't know where he came from or what he learned, so we assume he has no particular style or code of conduct. We can, however, assume that they will often bear similarities to each other despite the cultural background involved with their development.
Something to note about all this is that Shanks was a baby when the Roger Pirates found him. He wouldn't have had a chance to go to a school to learn swordsmanship. He was with them. If he did learn it, then he learned it from people like Rayleigh is what I'd assume. Rayleigh is a good teacher, but what kind of swordsmanship do either of them really use and what kind did Shanks adopt? What kind of values did they teach him as a swordsman? As a pirate, Shanks understands you can't say "that was unfair" if you lose a pirate fight, but swordsmen may say that in a swordsman's duel it's dishonorable to use things like subterfuge. In fact, that's how Oden got beaten by Kaido. He didn't expect someone to use subterfuge against him.
Subterfuge = using deceit to achieve goals
- Oden was deceived into believing Momonosuke's life was in danger, but this was the result of a Devil Fruit user's ability being weaponized against him the moment before he nearly defeated Kaido.
Subterfuge is highly against the honor code for bushido practitioners. It is a dishonorable act according to their beliefs.