Senridama

Named the Thousand Mile Jewel, the Senridama is a crystal invented by Bansui Amatsuki that lets its holder observe and project the movements of a faraway individual, reaching even across separate dimensions. It behaves much like an antenna, picking up and interpreting a target's spiritual pressure in order to reproduce their actions.

For the crystal to function, its operator must already know the person they mean to watch, that person has to carry a meaningful amount of spiritual power, and the user themselves needs certain abilities. Coupled with a Denreishinki, the captured images can be viewed directly on that handset. The Senridama itself is grown from a rare gas found only beneath Hueco Mundo. Soul Society once pursued such crystals but abandoned the work, wary of the danger a Hollow would pose if it gained one and began spying on Shinigami. Two safeguards exist against it: a medicine that briefly suppresses spiritual pressure, which Hanatarō Yamada gives Ichigo to slip out of view at the price of weakened combat strength, and cloth woven from Sodan-ito, or Blocking Thread, which hides its wearer from detection.

Bansui Amatsuki created the device and turned out copies in bulk through a dedicated processing factory, arming many Hollows with them. Three were once believed to exist, two of them sealed away. Ichigo Kurosaki claimed one after defeating a Hollow that carried it, while Shemihaza used Sodan-ito cloth to slip past the crystal Ichigo had taken.