We never found out how Hashirama died but here's a theori of mine.
In the fight against Kakuzu he mentioned that all konoha nins were as weak as their first hokage Hashirama, who he claimed to have fought. Is it possible that Kakuzu was the one who killed Hashi?
now i know kakuzu couldn't have taken hashi down easily but what if he attacked him after his fight with Madara? Nothing was mentioned in the manga about anything Hashirama did after that fight. what if all the people thought that the Hashi vs madara fight ended in a draw when actually hashi won and then got killed by Kakuzu?
In the fight against Kakuzu he mentioned that all konoha nins were as weak as their first hokage Hashirama, who he claimed to have fought. Is it possible that Kakuzu was the one who killed Hashi?
now i know kakuzu couldn't have taken hashi down easily but what if he attacked him after his fight with Madara? Nothing was mentioned in the manga about anything Hashirama did after that fight. what if all the people thought that the Hashi vs madara fight ended in a draw when actually hashi won and then got killed by Kakuzu?