The Kazaana was originally created by Naraku as a curse on Miroku’s grandfather, one that passes on through generations. The Kazaana appears on the palm of the wielder in the shape of a black hole. Eventually it will grow and swallow the wielder into oneself. The Kazaana can be damaged and expand unnaturally as well.Until then, it can be used to suck whatever is in front of it within the hole.
Miroku’s grandfather was actually deceived by Naraku who was dressed as a woman. Naraku pierced his hand and thus the curse began. Naraku explained that the curse would pass only to males in his family as long as their blood survived. His grandfather was swallowed by his own. Miroku’s father was swallowed by his but not before Miroku could catch a glimpse of his possible future. Mushin, a friend of Miroku’s father, has helped Miroku over the years to ease any pain or damage caused to the Kazaana.
Even though Miroku uses the Kazaana as a really good weapon, it has its downfalls. If any poison is sucked in, it can harm Miroku. Naraku has countered this attack by using the Saimyosho to stand by while the group is being attacked. If Miroku were to use Kazaana and swallow some of those bugs, he would perish.
It seems that the Kazaana is directly attached to Naraku. He has stated that the only way to get rid of the curse is to kill him. Once his demonic powers were reduced to almost nothing and the Kazaana disappeared from Miroku’s hand. When Naraku had regained power, it reappeared.