Soul bunshin or boo bunshin
Naruto experimenting with kage bunshin and remembering yamanaka technique was curious if it would be posible to using kage bunshin concept of cuting his chakra in half cut only his soul in half, so after experimenting with it he created soul bunshin (or boo bunshin) with work like this:
He can divide his soul in fragments and sent them from his body but with each divide his body is weaker let say he can pick up 30kg, when he divide his soul by 2 then he can pick up only 15kg and if by 3 then only 10kg, so using this he was training with the same training gear and when this is going to easy he divide his soul and do it again and again so much that there are more and more of his soul fragments and when he made them return to his body he gain all that power with mean if he can pick up 30kg and one of his soul fragments that were halved by three return he will be able to pick up 40kg.