all invented techniques can be traced back to an existing move/phemomemon, i am sure having known about rinne tensei made it more convenient to come up with edo tenseiBut it still doesnt explain how do you even start to create a jutsu like that. Tobirama is a smart man, i give him that. Coming up with an analysis and creating the signs and seals and figuring out how to apply those to a live corpse to reanimate a dead one is beyond that of a simple genius. Tobirama baffles me.
hiraishin being reverse summoing
rasengan being bijuu dama
of course doing it in practical might require years of observation/experimentation, chiyo who achieved something similar by giving a dead body/puppet her life-force and bringing him back to life said it took her years to develop it
(tobirama died after hashirama who was already a grandfather so he had no shortage of tme)
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its another tensei jutsu, which might explain why you need living bodies for edo tensei, you use the life force of a living person and bring back the dead