It might be a misunderstanding. Suppose there's a false rumor or misinformation that Naruto is a threat during the test. Sakura, being over - zealous in protecting the village or the test's integrity, decides to take him out. For example, if she believes Naruto has been secretly compromised by an enemy and she has no other way to deal with it during the test situation.
Perhaps she's under the influence of a new power or curse. In the world of fanfiction, new and strange elements are often introduced. If Sakura has been affected by a power that makes her see Naruto as a danger, even if he isn't, she could be driven to try and kill him during the test.
One possible reason could be a misunderstanding. Maybe she was misled by false information about Naruto being a threat to the village. Another reason might be that she was under some kind of mind control. In some fanfictions, dark magic or evil entities can take over a character's mind and make them act out of character.
Another reason could be related to a prophecy. If there was a prophecy in the fanfiction that Naruto would bring great destruction in the future, and Kushina, being a self - sacrificing mother, might think that killing him is the only way to prevent that destruction, even though it goes against her natural love for her son.
One possible reason could be that Naruto has some sort of new power that seems menacing or uncontrollable to Sakura at that moment. Maybe it's a power he got unexpectedly and it has some sort of dark or wild aspect to it that makes her blurt out 'demon'.
In some cases, Naruto might try to reach out to the Sakura he knows deep down. He could try to remind her of their past together, their training, and their shared experiences. He believes that the real Sakura would never do this, so he tries to break through whatever is making her act this way.
It could also be a form of self - protection. Wearing a mask might shield her emotions. Sakura has been through a lot, and like Kakashi, who may use the mask to hide his past traumas, she might be doing the same. For example, if she's trying to distance herself from her old self or past relationships that have caused her pain.
Maybe in this fanfiction she experiences a great loss, like the death of a loved one in a very tragic way. For example, if Ron or Harry were killed in a battle and she blamed herself for not being able to prevent it. This overwhelming guilt could be a reason for her to try to kill herself.
There might be some 'naruto is killed by sakura fanfiction' out there. One possible reason could be to explore a dark and alternative storyline. Maybe in that fanfiction, Sakura has been corrupted or misdirected in some way, perhaps by an evil force that makes her turn on Naruto. Another reason could be to create a high - impact, emotional story where the death of a main character like Naruto at the hands of someone close shakes up the entire Naruto -verse in that fan - created narrative.
Perhaps in the fanfiction, there is a plot twist where Sakura has been brainwashed by an antagonist. The antagonist could be using her to get to Naruto, knowing their close relationship. So, she would then be made to attack Naruto without her own will. Or, there could be a prophecy or some sort of pre - determined fate in the fanfiction's plot that causes Sakura to hurt Naruto, even if she doesn't really want to.
One possible reason could be his thirst for power. He might see Naruto as an obstacle in his pursuit of greater strength. Maybe he believes that by eliminating Naruto, he can prove himself to be the stronger one and gain more recognition in the ninja world.
Maybe the friend betrayed the village in a really bad way. In the Naruto universe, loyalty to the village is important. If the friend joined the enemy and was causing great harm, Naruto could see killing them as a last resort. For instance, if they were about to give away crucial secrets that would lead to the destruction of the village.