Beads of Subjugation

, called the Beads of Subjugation in the English dub, is the title of the prayer beads/necklace that Inuyasha wears around his neck. When activated by the use of a particular word, the beads glow and bring the wearer under control (in a manner of speaking). In Inuyasha's case, it's usually referred to as the "sit" command.

Purpose and History
Originally, it was Kikyō who was going to put the beads on Inuyasha in order to make sure he behaved. She told Kaede that she was going to trick him into wearing them by telling him they were a gift. She admitted it was a bit underhanded, but by this point, she had already decided she wasn't going to kill him, but knew he might still cause some mischief. She ultimately decided against it when he gifted her with one of his late mother's treasures: a shell of lipstick. While originally Kikyo had intended the key word to be "beloved," in order to subjugate Inuyasha, the later word had apparently became "sit."

Fifty years later, a desperate Kagome released Inuyasha from his seal so he could kill Mistress Centipede. Not three seconds after dispatching the demon, he turned on Kagome, intent on taking the Shikon no Tama for himself. She fled and he gave chase, prepared to do whatever he had to get it, even kill. During the pursuit, Kaede uttered a chant and the beads found their way around Inuyasha's neck. She then told Kagome to "say the word". Thinking of his dog ears, Kagome said "osuwari" (お座り), meaning "sit (to a dog)". The beads glowed and brought Inuyasha slamming to ground. (He was actually standing on a bridge at that moment, so he slammed straight down through the wood and into the water below.) From this point, it became a running gag throughout the entire series.

In InuYasha the Movie: Swords of an Honorable Ruler, a super charged "osuwari" caused the Kotodama no Nenju to more or less explode. Inuyasha went the rest of the film without wearing them, and a worried Kagome found herself wondering if she still had a connection to him even though he was without them. A scene following the credits showed Kagome tricking Inuyasha into wearing the beads again in very much the same manner Kikyō had planned to do. He continued to wear them for the rest of the series.

Attributes

 * Once they are placed on the yōkai or hanyō target, the Kotodama no Nenju can only be removed by the "word sayer". Try as they might, the wearer cannot remove, break or cut the beads from around their neck.
 * Only one person can activate the beads. Others have tried and failed, and Kaede, the one who put the beads on Inuyasha in the first place, has been shown asking Kagome to make him sit on her behalf.
 * Activating the beads causes the wearer to fall at high speeds and land agroof.
 * Even if the wearer is already down, the repeating of the trigger word pulls them further still into the ground and continues to cause pain.
 * As a spiritual artifact, the Kotodama no Nenju can have an effect on demonic energies within the immediate vicinity.
 * When Tessaiga was broken and Inuyasha kept reverting to his demon form, Kagome used the beads to not only knock him unconscious, but also to temporarily force his demon blood back into remission.
 * In Swords of an Honorable Ruler, the spiritual power from the activated beads is enough to drive off the demon sword Sō'unga, breaking its hold over Inuyasha and sending it rocketing away at high velocity.
 * Also in Swords of an Honorable Ruler, Rin threw a couple of the beads at a demon that was holding Kagome. The spiritual essence of two beads that hit its face was enough to melt its entire head into a sizzling nothing.

Manga vs. Anime
When Inuyasha was first commanded to "sit" in the manga, he was standing on land and was slammed to the ground. In the anime, Inuyasha was standing on a bridge. After repeated commands, Inuyasha's body broke through the bridge and fell into the river below.

Trivia

 * The trigger word Kikyō planned to use was "itoshii" (愛しい), meaning "beloved".
 * The word "osuwari" is a sit command used specifically for dogs, which is why the beads don't activate whenever Kagome tells him to sit down.
 * It's never clarified as to what happens when Inuyasha is in human form. Kagome is never shown to trigger the beads while he's human, nor is he shown to try and remove them.
 * In Inuyasha's case, the Kotodama no Nenju are pretty much the equivalent of a collar or a choke-chain, maybe even a shock-collar, considering he's a dog demon.
 * During the last scene of the 3rd movie, when Inuyasha attempts to remove them, they don't flash as they did in Episode 2. Kagome admits that she trusts Inuyasha, but refuses to remove them because she doesn't want him running off again (which is her only means of holding any authority over him).