Bats were used by Rinji. Rinji had the ability to use ultrasonic waves to use the Bat Controlling technique so that he could communicate with bats, and they could likewise communicate with him. He was able to give them orders, such as to search the area around him.
Once Rinji took control of his bats, he could command them to produce high frequency ultrasonic waves that affect the mind of the opponent. These bats proved to be an effective counter to the Crystal Release; the ultrasound waves moved at a frequency that broke down the crystal at a molecular level, allowing the dispersion of crystal particles back into the air.