We first saw this move when Kenshin was duelling against the child toyer, Raijuuta (manga). At that time, our poor boy was in dire straits, his upper right arm had earlier been hit by Raijuuta's Hiken (secret sword) which borrowed the force of the sword hitting against the air to form a vacuum so large it could travel forth and cut a person down.

So Kenshin brings Youtarou, standing behind him when the Hiken struck him to Megumi for treatment. He himself gets his hand bandaged and given some local anesthetic.

So his right hand is useless now. So what. With an opponent like Raijuuta, Kenshin says, one left hand would be more than enough...

So while Raijuuta continues gaining the upper hand by forcing Kenshin to stay out of distance, Kenshin yells that he could still achieve an out of distance attack... which is...

Hiten Mitsurugi Ryuu Battou-jutsu . Hi Ryuu Sen!

The action of Hi Ryuu Sen (Flying Dragon Flash) is actually as mentioned, a part of Battou-jutsu. That is, using the force of the sword leaving the sheath to increase the actual impact by 2 to 3 times. This skill does not involve a right hand movement but just waist power, arm and finger strength.

The point of all this was to push the sword out of the sheath using your finger as the way you used it to flick a coin, only this time, like shooting a dart.

Before Kenshin performed the actual movement, he did reverse psychology. Then, he put his right leg in front and swung heavily to his left.

Immediately after that, he swings back and slides his right leg forward into a front stance and with the repelled energy generated he transferred the sword's hilt onto Raijuuta's forehead. He finished off the movement, after the sword had already left the sheath, by stepping on his left leg. As the Hi Ryuu Sen is a move which utilizes the sword only to hit with the hilt, I presume it was not meant to kill, but to knock out the opponent, which was what happened to Raijuuta anyway.

Hi Ryuu Sen - II

The second appearance of the Hi Ryuu Sen in the manga was when Kenshin was duelling with Chou to try to save Iori. This time, Seiki Arai, son of Shakku Arai who was the one who gave Kenshin his first sakabatou was trying to get on the other side of the battle to retrieve his father's last sword and hand it to Kenshin.

So as he ran, Chou got frustrated and twisted his long and bendy sword after the man. It was stopped in time by Kenshin's Hi Ryuu Sen which pinned the force of the long and bendy sword onto a nearby vertical standing point.

This shows how powerful the Hi Ryuu Sen is, although the execution needs to be perfect to achieve this standard. In the match with Chou using Hi Ryuu Sen, Kenshin did not finish the movement with a step to the left. So it can be presumed that he did not fully utilize his full force because too, true, that he was also injured in the leg in that point of time already.