Kazaana

The, also known as the Wind Tunnel, was a curse placed on Miroku's grandfather by Naraku; it would go on to become Miroku's most famous technique. It appeared to be a black hole shaped on a person's palm. Once every year the wind tunnel grew larger and the wind became more powerful until eventually it swallowed up the unfortunate wielder. It has been shown that the wind tunnel can be damaged and expanded unnaturally.

History
Miroku's grandfather had his hand pierced by Naraku, who had disguised himself as a beautiful woman. After being branded with the curse, Naraku told him it would pass throughout every male in his entire family so long as he was alive. Soon after his son was born or in childhood, the Wind Tunnel swallowed him up as it developed over the years. Also, when Miroku was a child, the tunnel swallowed his father up and he was stopped from coming to his aid by his father's friend Mushin, who didn't want him to suffer the same fate as his father.

After meeting Inuyasha for the first time and battling him, Miroku showed him his Wind Tunnel and after telling him his story on how he got it, Miroku helped him and his friends by using it to suck up many demons, minus the poison-bearing ones like Saimyōshō and others.

When Naraku faked his own death in a bid to trap Kaguya, his demonic aura was reduced to the point where the Wind Tunnel disappeared. However, once he returned, so too did the Wind Tunnel. Once Miroku's Wind Tunnel had reached its limit, he was forced to use it sparingly. However, when Naraku had been reduced to just a head by Inuyasha's Meidō Zangetsuha, it started to close. After Naraku died when his soul was purified by Kagome's Sacred arrow and disappeared forever from the material world, the curse was finally lifted and the Wind Tunnel disappeared for good, allowing Miroku's life to be spared.

Yashahime
Miroku admits he relied too much on the kazaana in his youth and misses having its power at his disposal to deal with troublesome demons. It's because of this Miroku decided to train for 1000 days to obtain spiritual power that could rival it.

Uses and Effects
Although the Wind Tunnel was initially brought about as a curse, those afflicted with it have been able to tune this weakness into a strength. When fully exposed, the Wind Tunnel inhaled whatever was within range and banished it to a different dimension. Although Miroku could clear out large troops of demons this way, if he inhaled too much demonic power at once, he became tired to an equal extent.

Trivia

 * If someone cursed with the Wind Tunnel sucks in too much poison, they will expel a large amount of blood; likely their body's way of trying to get the poison out of their system.
 * As a result of the internal damage from very strong poison, they cannot handle sucking in the poison of weaker demons, causing them great pain.
 * According to the official guide book Zusetsutaizan Ōgikaiden (translated as InuYasha Profiles), Miroku's Kazaana can suck up to 600–700kg massive objects. Takahashi also added that if there is no obstacle during the functioning, the Kazaana would probably work more effective than usual. However, when compared with Inuyasha's Kaze no Kizu, whose maximum height of attacking enemies is up to 80 feet from the ground, the Wind Tunnel can suck up things which are 100 feet from the ground.
 * Additionally it was said that whatever gets sucked into the Kazaana is banished to another dimension. Thus making it somewhat confusing as to how Miroku has repeatedly gotten poisoned by sucking in Saimyōshō; creating a contradiction unless it was a mistranslation.
 * In the anime, originally, when Miroku opened the Kazaana, a flash of light would illuminate, perhaps meaning the seal coming undone. During the Final Act, purple energy surrounds the Kazaana's opening. Also, how the wind pulls in has changed; in the Final Act, it spirals inward, but before it did not.
 * In InuYasha the Movie: Affections Touching Across Time, the yōkai Ruri copies the Kazaana and later loses control of it. Her death demonstrated how Miroku's grandfather and father were killed when their Kazaana eventually breached the confines of their palms.