What about the promised koi transfer?

Zhang Shuntian was originally a celestial master. Later, his dependent grandmother was killed by an unknown creature, and his spirit was shocked. He thought he was dead and a zombie. He found his grandfather's collection of books and summoned monsters to avenge his grandmother. However, he drew the wrong formation and appeared. After buying a koi carp and signing the contract, the koi carp became Zhang Shuntian's master, so what about the koi carp being transferred?He just wanted to take revenge. Why did the ghost world open, the devil was born, the six worlds were about to collapse, and the contract was wrong?