Great Empress Heart Sutra

An administrator of the Lin family brought the soul contract forth.

It was an ancient scroll, made of a primordial strain's or a primordial true spirit's hide. The soul contract was engraved with complicated runes that specified the contract.

Surrounded by all the runes, there was a hideous ghost head image.

Upon seeing the soul contract, the Thousand Hand Granny sneered as she cleanly cut her finger with a dagger, dropping her blood onto the contract's ghost head.

After the ghost head came into contact with the Thousand Hand Granny's blood, it suddenly came to life and flew out of the contract reel, straight into the Thousand Hand Granny's heart.

This ghost head was a curse. Whoever signed the soul contract, and did not have the power to counteract the soul's curse, would have their hearts eaten by the ghost head and die if they were to breach the contract.