Well, one way could be if Naruto has some new, super - powerful jutsu that he's developed. Maybe he's found a way to combine his Sage Mode with his Nine - Tails chakra in a completely new and unexpected way that gives him an edge over Hashirama.
Another scenario could be that Naruto is in a situation where Hashirama is weakened. Maybe Hashirama has already been in a tough battle before facing Naruto, and Naruto, being full of energy and with his usual determination, is able to take advantage of Hashirama's tired state and defeat him.
Well, in a really dark and twisted fanfiction, Sasuke could be under some sort of mind - control spell. The spell could be so strong that it overrides his feelings for Naruto. He might then attack and kill Naruto without fully realizing what he's doing. But in the real Naruto lore, their friendship and mutual respect are so strong that this is highly unlikely.
In a fanfiction context, it could be possible through some creative plot devices. Maybe a powerful jutsu was used that altered their memories or destinies. For example, a rogue ninja with a forbidden time - bending jutsu made them believe they were in love and got married. It could also be due to some sort of political alliance gone wrong in a strange way, where they were forced into a marriage - like situation and over time, developed real feelings for each other.
In this 'madara kills naruto fanfiction', the scenario might be set up in a way that the world around them has changed. Maybe there are new rules in the ninja world that Madara has adapted to better than Naruto. He could be using the political or social situation to his advantage. Additionally, the writer may have given Madara a different motivation that makes him more ruthless and determined to kill Naruto, and through a series of carefully crafted events, he manages to achieve this goal.
Well, in a fanfiction, the writer can bend the rules of the original Naruto universe. Maybe Kabuto could kill Naruto if he somehow got hold of a super - powerful and unexpected weapon or jutsu that nullified Naruto's abilities.
Sasuke would probably be one of the first to support Naruto. They have a deep bond and Sasuke respects Naruto's strength. He would see Naruto's victory over Hashirama as a sign of Naruto's growth and power.
In some fanfictions, Naruto might defeat Zabuza through new jutsu. For example, he could develop a unique shadow clone variation that overwhelms Zabuza's water jutsu. Maybe he combines his Rasengan with some unexpected element, like wind chakra in a new way that Zabuza can't counter.
Another possibility is that Naruto could defeat Kakashi if the latter was in a weakened state. Maybe Kakashi had just come out of a tough battle with other powerful enemies and was low on chakra. Meanwhile, Naruto was at his peak, full of energy and ready to fight. In this situation, Naruto's sheer determination and his own strong abilities could lead to his victory.
Well, one way Naruto could defeat Iwa in fanfiction is through strategic alliances. He could team up with other ninja villages or powerful individuals who have a grudge against Iwa. Together, they could plan elaborate attacks and outwit Iwa's military strategies. Also, Naruto's ability to inspire others might lead his allies to fight more bravely, giving them an edge in the battle.
One possibility is that Naruto discovers a new power or form that gives him an edge. For example, he might combine Sage Mode with a new type of chakra control that allows him to overpower Madara.
It could be a long - lost relative of Hashirama. Maybe a distant cousin or a descendant from a hidden branch of the Senju family. This character would carry the bloodline of Hashirama and thus have the potential to inherit his powers.