Hollows by definition are lost souls that have lost their chain of fate, and that determines a soul's final destination within the PH universe. Either they go to the Soul Society to live in everlasting peace and happiness, or they lose what is important to them, becoming a hollow, one who's lost all physical and mental reasoning, replaced only by one thing: The urge to feed.

This ball is specifically designed to capture a variety of hollows, ranging from Gillian all the way to some Adjuchas, although those will require significantly more work to obtain.

The ball functions as a result of the Doctor's research into the nature of Hollows. Essentially, the ball rewrites the part of the Hollow that has lost its soul chain. Where this part was, a kind of 'Inhibitor' is replaced, causing a shadowy, purple-mist like presence to take up residence in that hole. As hunger is the only emotion that most Hollows understand, this 'inhibitor' serves to satisfy or intensify the feeling of hunger that the hollow is undergoing when given an order by the owner of the ball.

Additionally, if the hollow who has been marked by this ball should attack the owner of it, the mist will pierce through them painfully, paralyzing their body and dragging them back into the ball, as if pulled in by gravity.

Once the owner of a ball has successfully capture a hollow, it is registered on the inside of that ball, and the inhibitor's actions will make it easier for the hollow to understand that the ball's owner is now their 'master' and they could be disciplined if they disobey.

Generally, like all animals, you need to build genuine trust, and hollows captured by the ball are no exception. At first they'll be hesitant on following her orders but over time the owner can establish enough trust with the captured hollow to command it to use abilities like Cero, Acidic Touch, and regeneration. It is possible, of course, for one of the captured hollows to be defeated, and if a Shinigami or Quincy destroys one of these hollows, then the failure to connect with the registered hollow causes the ball to overload, self-imploding with a small amount of force.

Interestingly, this ball is only able to be used to attempt to capture and register a hollow at night, making it a bit limited in that regard.