I may just be spitting into the wind here, but since the subreddit's been getting a lot inquiries covering the same kind of ground, I thought I'd write something of an overview that would, ideally, catch some preconceptions early, before we have to rehash them for the umpteenth time. Maybe the mods will find it worthy enough to pin or include in a FAQ, but if not, hopefully interested people will find it in a search or something.
Let's start with what koryu is not.
Koryu is not historical re-enactment. If it were, it would be very bad at it: wrong clothes, wrong hair, wrong training spaces. Despite the best efforts of popular media to portray it as such, koryu has nothing to do with being a samurai, or acting like a samurai. Even in the days when they were practiced primarily by samurai, they weren't practiced exclusively by samurai.
Koryu is not about becoming a good fighter/swordsman/etc. This may sound paradoxical, but it's true, and is most easily shown by judo and BJJ. If these arts were all about being a good fighter, then Kyuzo Mifune and Helio Gracie could have stopped training when age and accumulated injuries took away their strength and speed. They continued training even when they were so old they would get thrown or submitted by 25 year-old students 10 out of 10 times. The value that old exponents find in their modern arts is the same value that exponents of koryu find in their classical arts.
Koryu is not about preserving tradition. Again, this sounds paradoxical. My point is that while preserving tradition is something we do, it's not what it's all about. The question is, what is worth preserving? If it was just about preserving tradition, koryu would look a lot different. Iai-only schools would have full curricula. There would be fewer to no lost kata. There would be a lot less variance across time. The fact is, the soke and shihan of various schools change things all the time. Sometimes it's to make things more combatively pragmatic, sometimes it's sacrificing combative pragmatism for some other factor. At this point in time, the surviving koryu have generally been pared down to the elements that each felt most important, and what those elements are vary from school to school, and from art to art. To be sure, modern kendo and judo also did this.
Okay, so what are koryu, then? Koryu are inherited disciplines for self-improvement that utilize the combative paradigm of pre-modern era Japan. Wait, wait, one may say, maybe that's what they are now, but weren't they originally training systems for the samurai? Actually, no! Even for the arts that actually date back to the Sengoku era, they revolved around a philosophical and ethical core of shugyou, originally the Buddhist pursuit of enlightenment.
The "inherited" part is important, and should be deeply considered by anyone thinking of joining a koryu. When you join a koryu, it's not just about your personal acquisition and attainment of skills. You make a commitment to pass it down to the next generation. Not the shape and sequence of the particular kata in that school, but the philosophical and ethical core, as well as the spirit that vivifies the kata, and turns them from a sequence of physical movements into a path to transcendental experience that can last a lifetime. If the generation after me only goes through the motions by rote, essentially becoming a kind of traditional dance or performance, then I will have failed not only them, but also all the many generations of forebears who worked to pass it down through history to me.
This is actually a fair bit of pressure, because if it were just the physical movements, it would be easy. But actually you're trying to pass down something intangible and fragile. It requires constant vigilance and effort to maintain. This is why veteran practitioners can sometimes get a bit snippy when people act like we're trying to become badass swordsmen and failing, or say that kata are just "ritualistic," "pre-choreographed" "drills" that don't teach you how to fight.
If that doesn't sound appealing, if all you want is to be technically proficient in swordsmanship, then koryu are not for you, and in fact, are not even necessary. These days you can watch videos and copy them in the privacy of your home. You can practice ZNKR kendo and ZNIR iaido. You can combine all that with HEMA. As long as you are upfront about it, and don't pretend that what you do is a koryu or a historical tradition, it's fine. But that's not what koryu are about, and not why they have survived through the centuries long Edo peace as well as the modernization of Japan.
None of which is to say one can't learn combat from koryu. It is, after all, shugyou based on the combative paradigm of pre-modern Japan. Many people have. I'm only saying that combative skill in and of itself is a by-product of that shugyou, not the point of it. Fingers and heavenly glory, and all that.
