Wandenreich Medallion

The Bankai Ensnaring Device (卍解籠絡設備, Bankai Rōraku Setsubi) is an object used to seal away a Shinigami's Bankai. Muramasa Neikan modified the device to seal Resurrección as well.

Overview
It is a convenient seal, taking the form of a badge, which can be used to block the Bankai of a Shinigami. It seems to be only able to seal one Bankai at a time. It also seems that other users of the device can detect when another user has used the badge on a Bankai user.

Modifications
After being brought to the Impero Nascosto by former members of the, Muramasa then mass-produced the badge, allowing it to be used by many of the members of the Impero Nascosto against their foes. He also modified it to allow the badge to have a similar effect on the Resurrección of an Arrancar. It still has the "one use" rule applied to it.

Trivia

 * It has never been named in the manga, therefore the article is subject to change.