By either inserting his poisonous chakra, implying a seal through either physical contact, or through his eels either by their fangs or through physically restraining the target, Isamu is able to place a unique and powerful seal onto his opponent. The seal has given Isamu the ability to control his opponent's osteoblasts (cells responsible for producing bones); the ability to control their osteoclasts (cells responsible for breaking down bones); the ability to regulate their bones'. Hence the name, the seal will begin to break down the bones opponent's body. In one's body, the skeleton works very closely with the muscular system to help you move. Without the bones of their skeleton, they would be a blob of water-filled tissues. The bones create a framework to which your muscles and organs can connect, causing their body to eternally collapse, though death could ensue, it is not common. The effects of the technique are permanent unless Isamu reconstructs his opponent's bone structure. Even after an ally of the opponent removes the fuinjutsu seal, it does not reverse the effects of the Jutsu, only removing Isamu's ability to control his opponent's osteoblasts. Advanced medical ninjutsu would be the only way, in which an opponent could gain back their bone structure.