Gravity weights they do the same thing as weights but they improve nin and gen instead of stamina and taijutus
this doesn't make much sense... how can weights raise someones nin or gen?
or they could make something like water walking except make it so it can raise nin and gen.. maybe something like... erm.. i have no clue..
why not have something to boost water training faster.... Make it expensive.... how about 150k? xD