Hoshi No tama is one of many abilities possessed by Kitsunes in the novels series to generate a "star-ball" that can store their memories and also acts as their life-force. It is a powerful object bound to a tree that can be used by kitsunes used to open a portal to the Dark Dimension.
The size of a kitsune's hoshi no tama appears to be proportionate to the size of their power.
In the novels, Misao, Shinichi and Inari all have their own star balls. In The Return: Midnight, Damon uses Misao's star ball to reopen the gate to the Dark Dimension and takes Bonnie with him by accident. Shinichi buys Bonnie to extract information about Misao's star ball. Since the group has drained Power out of it, Misao is dying. Damon and the 3 others go to the Nether world to get the biggest star ball ever made in hopes that it will save their town. In there journey, Shinichi and Misao die.
The kitsune they are working for Inari, Isobel's grandmother. She is the most powerful Kitsune in the world, and the star ball is hers. In the Nether World, on the smallest moon, the group finds the star ball in a tree. Damon is killed when the tree stakes him in the heart while he saves Bonnie from falling to her death. Elena uses her "Wings Of Destruction" to destroy the tree and star ball, killing Inari.
In the novels, Kitsunes are linked to their star ball if it gets destroyed, they die.
Depictions of kitsune or their possessed victims may feature round or onion-shaped white balls known as hoshi no tama (star balls). Tales describe these as glowing with kitsune-bi, or fox-fire. Some stories identify them as magical jewels or pearls. When not in human form or possessing a human, a kitsune keeps the ball in its mouth or carries it on its tail. Jewels are a common symbol of Inari, and representations of sacred Inari foxes without them are rare.
One belief is that when a kitsune changes shape, its hoshi no tama holds a portion of its magical power. Another tradition is that the pearl represents the kitsune's soul; the kitsune will die if separated from it for long. Those who obtain the ball may be able to extract a promise from the kitsune to help them in exchange for its return