(So, I don't have an in character reply but I want to know if there are any requirements on the creation of a new Jutsu, the details of which you already know. It would be an active Jutsu that continuously drains chakra in order to boost weight on parts or the whole of the body. Chakra itself can cause pressure changes and move objects so I could easily justify the physics of such a thing, and it could potentially be adapted to reduce weight as well.)