Board Thread:Naruto Discussions/@comment-26708623-20161103030058/@comment-4134125-20180729233627

Sorry for replying 2 years too late, I, however, think that it happened as follows:

1) Hashirama's death: Hashirama died in a battle during the 1st shinobi world war. Madara must have somehow manipulated/controlled the remaining kages, thus instigating the war. Hashirama could be killed facing all the first kages along with tailed beasts under their control, with possibly just first kazekage and the tailed beasts surviving the encounter (because, according to a databook, he was killed by an assassin). Madara could have been there as well, though masked.

2) Tobirama's, Kinkaku's and Ginkaku's death. At the end of chapter 526, Ginkaku says "Pitiful, snared by the second hokage, when we beat him before, eh, Kinkaku?" -> Huge implication that those 3 got killed together. Ambushing Tobirama and second raikage while using six paths items to bring Tobirama close to his death is very probable, but because Tobirama is so intelligent and strong, there is no way he would be defeated by a mere "Kinkaku squad" composed by 20 ninjas. There must have been Kinkaku, Ginkaku and, possibly, a third raikage (the only survivor of the battle).....

I can't really see any other way how Hashirama and Tobirama could have died.