Gensui creates a special sealing tag which if placed on human beings, transforms them into false replications of one of the tailed beasts. Not only does the seal shape the victim into the desired tailed beast, it also grants them the original's abilities. The tag can also replicate the tailed beast's jinchūriki as well.
In order to maintain itself, the technique drains the victim's chakra, leaving them in varying stages of incapacitation, dependent on the technique's duration. Also, while the technique is active, the victim is under the complete control of the user.