Hyōheki Seal

A sealing jutsu developed by the Mizuno Clan many years ago. It is often used to seal Yamiyoryu inside its host. The seal does not allow the creature's chakra to merge with the chakra of the host, thus preventing the host from undergoing any transformation into the beast. However, this seal is not meant to be used on shinobi. The massive usage of chakra that goes along with being a shinobi puts a great strain upon the seal, weakening it over time.

In the case of Amaya Mizuno, the seal has weakened to the point in which is has become dangerous for her to utilize any jutsu or even move more than absolutely necessary. Due to how weak the seal has become, Tsunade has ordered that the seal containing the creature within Amaya be changed to the seal that currently holds Kurama within Naruto.