The wiki says that Hashirama died shortly after the creation of Konohagakure. Do we know how he died? I mean, he was powerful enough to stand up to Madara, so I feels like it would be no small thing that could kill him.
It's unknown exactly how did he die, but here's what we can find. His wiki page says:
Hashirama died shortly after the founding of Konoha in one of the many wars that were raging during this revolutionary era, but not before passing on the title of Hokage to Tobirama.1
However, if we head to the Konohagakure wiki page, we will find a more specific note:
Hashirama died during the First Shinobi World War, necessitating his brother Tobirama Senju replace him as Second Hokage.1 Tobirama would also die during the war, appointing his pupil Hiruzen Sarutobi as his successor before sacrificing himself to ensure his pupils' escape from Kumogakure's ninja.2
Now, here's what we know about the First Shinobi War (emphasis mine):
The First Shinobi War was the first of the great wars that involved the majority of shinobi villages and countries. The war started not long after the system of one shinobi village per country was established by the founding of Konohagakure. To try and maintain a balance of power, the First Hokage divided the tailed beasts among the other five villages3 when he began his peace talks with them.
So it indeed looks like he died in the First Shinobi War, which is not too surprising, considering that
his brother - the Second Hokage Tobirama Senju - died in the same war2, in which other Kages and Tailed Beasts were involved.
- 1 Character Databook 1, page 116
- 2 chapter 481 pages 4-10
- 3 chapter 404 page 14
In my opinion, the First Hokage is meant to be a more mystical aspect throughout the series.
They start off at a very early point in the original Naruto series explaining how powerful he was, and they reference that continuously more and more throughout the series. The same can be said for the Sharingan. Orochimaru is obsessed with research concerning both if them, and we see plot developments all throughout the series with both of them.
My theory is that Hashirama was killed off in order for these plot developments to occur. Unfortunately we don't have much information on this, but I think that the reason why it's so gray in that area is to allow for future plot developments to happen.
Obviously the First Hokage was incredibly powerful. Madara even goes so far as to say that even with his Rinnegan/Eternal Mangekyo/Mokuton jutsu, he still wouldn't be a match for Senju Hashirama. It's kind of hard to believe that he died in a random shinobi battle.
Lets not forget that Hashirama's Mokuton-infused cells granted Madara an enhanced life span, but they also grant insane chakra-reinforced strength and chakra-enhanced abilities. With Mokuton cells, Danzo was able to use Shisui's Kotoamatsukami once every four days, rather than once every 10 years.
We know that he is dead during to Orochi and the Third's battle. So maybe he was killed by a random group of vague assassins that never get mentioned again in the series. If that's the case then that is one big gray splotch on an otherwise colorful canvas. Because if there is one thing I've come to respect out of Naruto, it's the writers attention to detail and the complexities of the series... Not some half-assed plot tie up where the most powerful ninja in the known world gets vaguely killed in the first shinobi world war.
It says that he died sometime before or at the early stages of the first shinobi war, Tobirama also died during that war and Hiruzen became Hokage then
During Orochimaru's reanimation of the 1st hokage, based on the reanimation he's still wearing a combat armor which means he's in a middle of fighting, neither assassinated, sacrificed for something or died because of some reasons.
Or maybe since he's also one of Orochimaru's primary subject's for experimentation, Orochimaru might have done something on the 1st's body, he might have poisoned it or something.
No one really knows this is just only my theory.
But if our theories isn't still right the death of the 1st hokage still remains a mystery
I believe that Hashirama's story is a lot colder, different and more true to his character, then what people presume. Hashiramas life was an extremely difficult hardship to bear and not anyone could just be, what he was. When I say this, I don't just mean physically but emotionally and mentally, as well. He spent his life, trying to juggle peace, family, friendship and justice for everyone. He was constantly being tugged by opposing opinions of what peace truly was, or what kind of consequences would come of his actions as a hokage....who would it benefit? who would it hurt? Would peace truly come of all this, between the Senju and Uchicha clans....or any clans!? I believe that Hashirama became tired of it all. He coudlnt balance all this - and no matter what he did, true peace would never come of all his goals. When Madara read the Naka Shrine; he found out that true peace just wasn't possible; for it was all an endless cycle of death and hatred between clans. After much time and many years of Hashirama fighting, fighting and more fighting - he started to understand what Madara was trying to say but could never get to that extreme of an solution. He probably couldn't convince himself of what was right and wrong anymore. True peace was a catch-22. There was no way to really reach it. This could've had a big part to do with Hashiramas standards of peace, since they were so high. He couldn't bear the fact that he failed(at least by his standards), and like he always says "conflict, no matter what the era". Even the most powerful people in the world have a limit. His heart could only take so much killing and blood spilling. Think about this: A man who speaks of nothing but peace and love....seeing nothing but war and hate. The Hashirama that we all know, was a genuine human being with a soft heart and eventually that heart cant take anymore pain. Yeah, im saying it, because this is what I believe his character truly reflects: I think he let himself die in war -or- killed himself. He was just tired of it all and saw no more purpose or meaning, so he hands the title to his brother and goes off to war with the intention of dying without people knowing it was premeditated. Maybe he wanted people to learn a lesson from his death, if they could figure him out. A great and extremely significant character like Hashirama, has to have a very significant death, not just by dying in battle. He was either truly depressed of this fate that could not be altered by his leadership and skills.....or......he wanted his death to be something that people could learn from. He figured, he goes out with a mark on the world. His death maybe would be another component of people in the future finding something more close to true peace. All his successors would learn from him.