Tail Ring

The Tail Ring is a device used to keep Rin Okumura in check. Usually attached to the base of his tail, it is a benign implement that doesn't interfere with his actions, but when required, his keeper chants the Rokuji Myouou in order to tighten the ring and paralyze Rin with pain to the point of unconsciousness.

Trivia

 * The tail ring seems to be based on the headband of Sun Wukong in the Journey to the West, sharing a similar appearance and function.