Hi,
Which Ryu teach Yoroi techniques? Well, all of them/none of them, really. Most of the techniques can be interpretted in yoroi kumiuchi (armoured fighting) fashion, as well as the more commonly explored suhada (unarmoured) style. But to take the histories of each school into consideration, let's look at each in turn:
Gyokko Ryu is said to have been founded around 1162, at a time when the style of armour worn was what was later called O Yoroi, designed to be worn on horseback, and not very useful for fighting on foot. One interpretation I have come across for Gyokko Ryu postures utilising 50/50 weight distribution more than the other schools is this armour, as it is heavier and a little more top-heavy than later versions. And if you look to the targetting used in Gyokko Ryu, it has a prominence of striking to the arms (which had no armour), kicking up under the legs (which had little to no armour), strikes to the shoulder joint (a weak point in armour, at the shoulder straps), and direct strikes to the face (usually unprotected).
But it also has techniques such as the Shime Waza, which appear to be purely unarmoured, as well as strikes to the side of the neck (with shuto ken and boshi ken). When a Kabuto (helmet) is worn, striking to the side of the neck isn't always possible/easy, so that may be a re-interpretation of striking to kasumi (the temple), which, in a helmet, can be very disorientating (particularly as you often don't see it coming). The boshi ken, though, is more likely a grab-and-pressure, and we'll deal with that in the other schools. So Gyokko is probably armoured, with some unarmoured added as time went on.
Togakure Ryu is from about the same time (1185), and it's origins include Daisuke Nishina fighting (as a samurai) on the battlefield, so the use of armour is not exactly foreign to this school. However, as time went on, it became a non-battlefield art, focussing instead on the avoidance of conflict, with each technique involving evasion and escape (with metsubishi). I personnally feel that Togakure Ryu is designed to be trained/used in either regular clothing or very light armourments (kogusku), possibly against lightly to heavily armoured guards.
Striking is typically to the limbs, with body strikes to the solar plexus (suigetsu), or under the right arm. With light armour, the front of the body was often protected, with the sides left open (to keep the weight of the armour down), and with full armour, the join in 95% of styles is under the right arm. This is a callback to the original O Yoroi, where the body is covered front, left side, and back with a solid peice, and the right side is covered by a separate plate. This is due to the fact that it was designed to be used on horseback, when firing arrows. The right arm draws back, and is therefore held the furthest from the enemy, and is the safest place to have a weaker joint.
Koto Ryu is also from a period of intense war, dating from 1562, in the middle of the Sengoku Jidai. The techniques of this school are primarily striking, with only a little grappling. This is unusual for a Japanese school, as they tend to favour grappling over striking, due to the fact that hitting metal often hurts. Koto Ryu, however, is different. But, of course, this is based on the way it is trained today. My belief is that it was originally far more "grabbing" than striking, with fists such as Shako Ken being utilised as a grab to the base of the throat (the nodawa, the protective plate over the throat that Dale was refering to), or the face/face-plate (menbu) before kicking. With this in mind, Koto Ryu is very well-placed as an armour school, with the striking approach being better suited for unarmoured combat.
Shinden Fudo Ryu Dakentaijutsu. This section involves an entire part based on suwari waza (seated techniqes), in this case from fudoza no kamae (called za no kamae in this school). Typically, I would say that seated techniqes are non-armoured, but if you are going to sit in armour, fudoza is one of the main methods you would choose (a half-seated posture is the other main one). The majority of techniques tend to swing from armour based to suhada quite often, making me think that this school, maybe more than the others, has gone through quite a bit of change over it's history. Nichi Geki, Gekkan, Setsu Yaku and Karai seem very armour-friendly, while Fubi, U Ryu, Hibari, and Mu San are techniques that I wouldn't want to rely on in heavy metal armour.
Shinden Fudo Ryu Jutaijutsu, on the other hand, is much more purely armoured combat. There is little in the way of striking, but some very big, heavy, dumping-style throws. The nage waza in this school rely little on lifting, relying more on pressure and position to break down the opponents balance in a way that allows you to dump the opponent in a very damaging way, in fact the throws can be made even more damaging when performed in armour.
Takagi Yoshin Ryu is possibly the most non-armoured art in this list. It is said, amongst other things, to have been a bodyguard school, and has quite a number of techniques where the opponent is thrown in a way that doesn't send them very far away: the idea is that if you are applying the techniques indoors, you don't have the room to throw them far. It also includes a section on Daisho Sabaki, as well as a dedicated section on Shime Waza, both of which are designed around regular clothing.
Kukishinden Ryu Yoroi Kumiuchi Dakentaijutsu. This is the big one, and may get me in a little bit of trouble if people haven't come across this theory before... Kukishin Ryu was originally a weapons-school, and after contact with Takagi Ryu took on a version of the Takagi Ryu Jujutsu syllabus for it's unarmed techniques. At this point, the Kukishin Ryu lost what was left of it's original unarmed combat. Many generations later, Takamatsu Sensei had inherrited a number of branches of what was left of Kukishin Ryu, as well as Takagi Ryu. He met with the then-current head of the Kuki family, and was granted access to their records. From his experience, and this new knowledge, he began to put the school back together. At the time, both Karate and Judo were gaining a great deal of prominence in the martial art community. Takamatsu and a colleague/associate of his, Ueno Takashi, a highly skilled and experienced master of several classical Japanese martial arts himself, both decided that they wanted to create an answer to thiese new arts. Ueno went on to create the Tenshin Koryu, and Takamatsu Sensei created the techniques for Kukishinden Ryu Dakentaijutsu.
The other version of the history of this section is that it is from a branch of the school Takamatsu inherrited, which he brought back into the school. In this version, the techniques are also refered to as Yoroi Kumiuchi, which literally means Armoured Close Quarters (Fighting). The techniques are similar to the brutal throws and takedowns of Shinden Fudo Ryu Jutaijutsu, and will work quite well in armour; in this version, this is the most pure armour-fighting in the Bujinkan system. The weapon techniques, of course, are primarily armour based as well (look to sword kata such as Kiri Age for thrusts and cuts under the right arm again...).
Gikan Ryu, Gyokushin Ryu, and Kumogakure Ryu have each been rarely taught, so not much can be said definitively about them. However, Gikan Ryu has stories about a number of it's heads and members being involved in battles, so I would be confident that armour based knowledge forms at least part of it's syllabus.
As I said, though, it will come down to how you train the various techniques. For example, if you are training Kukishinden Ryu as suhada kata, then you will use the boshi ken and koppo ken strikes as strikes, however, if you are training them as yoroi kumiuchi, striking with the thumbs into someone wearing metal clothing can result in damaging your own thumb. So these techniques are performed with pressure into weak joints in the armour, and various kyusho points on the body to give you the opening for the rest of the kata. In fact, I personally believe that this is the way boshi ken were originally used, and the idea of striking with them is far more recent.
DISCLAIMER: The views expressed above are mine, and mine alone. They are based on my personal exploration of the above schools, as well as other arts that originate from the same times (if possible). The evidence for these views are circumstantial bsed on the histories of these schools as I understand them, and may be totally incorrect. However, I hope that you may get some new ideas from this little stream of thought...
