Hiten Mitsurugi Ryuu
Kenshin learned how to be a swordsman from Hiko Seijuurou, the master of the Hiten Mitsurugi school, "Hiko Seijuurou" being a titular, hereditary name for the current master. The technique of the Hiten Mitsurugi school seems to be very difficult to beat due to the fact that it was designed for facing many opponents at a time. The key to Hiten Mitsurugi's techniques is extreme, god-like speed more than strength. The Hiten Mitsurugi school is extremely efficient and, as Kenshin often says, extremely lethal without the reversed edge sword.
Hiten Mitsurugi Ryuu has moves themed around "heaven" and "dragons," strangely appropriate for the lightning-fast, jumping (almost flying) moves Kenshin produces. Also, according to Hiko, Hiten Mitsurugi battou-jutsu are special battou-jutsu moves in that there is always room for a follow-up strike in case the first one misses. In his words, all Hiten Mitsurugi battou-jutsu involve two steps -- apart from the drawing of the sword. Most of the techniques are guaranteed to make opponents go "WTF?!" as Kenshin pulls the most improbable things. Apparently, the original, founding Hiko Seijuurou was very creative.
The Techniques
Do Ryuu Sen Kenshin strikes at the ground, rocks fly, and a shockwave follows. FFVIII players should recognize this as somewhat resembling Squall's Rough Divide limit break.
Hi Ryuu Sen Kenshin flicks the sword out of its sheath with his left thumb. The sword flies through the air hilt-first as a projectile attack. I have to say...Kenshin must have a really strong thumb.
Kuzu Ryuu Sen This is similar to the Ryuu Sou Sen (see below), as a flurry of blows, except they are directed at the nine vital points. This is a very fast charging attack in which the nine blows are almost simultaneous. It is used in determining if the student is worthy of learning the ougi (succession technique).
Ryuu Kan Sen A spinning, sweeping blow. It supposedly uses centripetal/ centrifugal force to add to the impact. It is usually dealt from behind, hitting the enemy's back, although the starting position is from in front of the enemy and is useful as a follow-up to a dodge.
Ryuu Kan Sen ~ Arashi Same concept as above. However, the force this time comes from Kenshin somersaulting. The blow is directed downward, instead of from one side.
Ryuu Kan Sen ~ Kogarashi Same concept as Ryuu Kan Sen, only targeting the head/ neck.
Ryuu Kan Sen ~ Tsumuji This time, Kenshin himself spins (tsumuji, lit. "screw" or "spiral") parallel to the direction of the attack, and delivers the blow. Same concept as Ryuu Kan Sen.
Ryuu Mei Sen Kenshin's nasty surprise for Enishi. The opposite of lightning-fast sword-drawing, this is lightning-fast sword sheathing. Sheathing the sword at a high speed results in the vibration of the sword and sheath. This is apparently so fast that it produces a high-pitched sound that's deafening (and damaging) for someone with heightened sensitivity of hearing. The vibrations are awful enough to destroy an opponent's sense of balance. For added effect, the sheathing is performed just as the opponent is attacking, while sidestepping the blow so that Kenshin's sword and scabbard are by the opponent's ear.
Ryuu Shou Sen A blow dealt from below, striking the flat (or edge) of the blade upward into the chest, stomach, or chin. Useful against tall enemies. Kenshin often augments the force by supporting the flat of the blade with his fist and by jumping.
Ryuu Sou Sen Kenshin deals a rain of blows at a very fast speed. This looks like a wild type of attack.
Ryuu Sou Sen ~ Garami Same as above. So far as I can tell, the difference is a matter of aim. This move is targeted at the head, shoulders, and neck. Also, the blows are more of slashes.
Ryuu Tsui Sen Kenshin first jumps into the air then brings down the flat of the blade of his sword on his opponent's head or shoulder from above as he falls. Kenshin's favorite move or at least the one he seems to use an awful lot. This simple-seeming technique alone is often enough to bring an opponent to his knees.
Ryuu Tsui Sen ~ Zan Similar to the one above. However, instead of striking with the blade, Kenshin pierces the target with the sword downward, resulting in instant death. Kenshin only used this during his Battousai days.
So Ryuu Sen A sword strike followed by a strike by the sheath. The sheath is held in a reverse position (sort of like Aoshi's grip on the kodachi when he's doing Kaiten Kenbou Rokuren
So Ryuu Sen ~ Ikazuchi The reverse of the above. Kenshin strikes or blocks with the sheath, and while the opponent's sword is thus engaged, he strikes with the sword. The sword may already be drawn, or it it may be drawn while blocking.
Amakakeru Ryuu no Hirameki The ougi or succession technique of the Hiten Mitsurugi School. It is the only counter to the Kuzu Ryuu Sen. In this highly dangerous technique, Kenshin adds an extra step with the left foot before drawing the sword as in normal battou-jutsu. This extra step adds a dash of speed (please, I'm trying to drive away images of Ryoma's split step from Prince of Tennis here) but also adds a dash of risk, because Kenshin risks cutting himself with the sword at this point (the sword is sheathed at the left hip, if you'll recall, and Kenshin's reversed-edge sword has the sharp edge facing him instead of out). In addition to this, the force from the strike is so great that it "creates a vaccuum" and draws the opponent forward and into a second strike -- if he manages to dodge the first.
Obviously, the Hiten Mitsurugi School is very dangerous for both the masters and the students. The succession technique can only be learned if the student is able to defeat his master by figuring out the Amakakeru Ryuu no Hirameki by himself. If he is unable, the student could die in the attempt. If he succeeds, his master would be the one to pass on and he will become the new master, which is why the Hiten Mitsurugi school is passed down a straight line. There can be no more than one master teaching the techniques at a time, and no more than one student. Which is a good thing, if you can imagine hordes of men capable of doing the Amakakeru etc. What if they started feeling competitive? Do the words "massacre" ring any bells?
Though technically Kenshin achieved mastery, he denied the cloak of the master and gave it back to Hiko. Maybe out of nobility, but, er, more likely out of aesthetics. It was too big for him, it ate him up. Plus, it was a weighted cloak, which restrains the master's strength just enough to prevent him from doing too much damage. Which says a lot about the Hiten Mitsurugi Ryu and its ideals, don't you think?
Kenshin, after doing this, is basically tossed out of the school. (Let's say it was an honorable dismissal rather than an expulsion, though.) Mastering the Hiten Mitsurugi school did not come without a price, however. As the Amakakeru Ryuu no Hirameki needed great strength behind it, the technique is best suited for big men -- which Kenshin is painfully not. In the final volume, we learn just what the consequences of his decision to use the technique in battle were: that is, irreparable, irreversible damage to his body that would only worsen with time.