One possible motive could be envy. Maybe Nott is jealous of Draco's relationship with his familiar and wants to hurt Draco by taking away something he cares about.
Another reason could be that Nott mistakes the familiar for something dangerous. If the familiar has some sort of unusual or menacing appearance, Nott might think it's a threat to himself or others and act preemptively to kill it.
Draco might be extremely angry. He could immediately seek revenge on Nott, not caring about the consequences. His anger would be fueled by the loss of his familiar, which was probably very dear to him.
One possible motive could be that Minato is under some sort of dark magic or mind control. In fanfiction, authors often play with the idea of characters being forced to act against their true nature. So, if Minato is being controlled, he might end up doing something as extreme as killing Naruto.
One possible motive could be that Harry is under the influence of a dark spell or curse that makes him lose control of his actions. In some fanfiction scenarios, dark magic can overpower a character's true nature.
One possible motive could be self - defense. Maybe Ares was about to harm Percy's friends or family, and Percy had no other choice but to fight back and end up killing him.
One possible motive could be a misunderstanding. Maybe Hercules is framed for something really bad, and Percy, believing the false information, decides to take action. For example, if there's a plot where Hercules is made to seem like he's about to destroy a city full of innocent people, Percy might feel it's his duty to stop him, even if it means killing him.
One possible motive could be a misunderstanding. Maybe Haku was disguised as someone else who was about to attack Naruto or his friends, and Naruto reacted in self - defense without realizing it was Haku. Another could be that in this fanfiction, Naruto has been somehow corrupted or influenced by a dark force that made him lose his normal judgment and attack Haku.
Perhaps in the fanfiction, Percy is forced into a situation where he has to choose between Thalia's life and the safety of many others. If the situation is presented in such a way that killing Thalia seems like the only option to save a large number of people, he might be pushed to do it. It could also be related to some prophecy that Percy misinterprets. If the prophecy seems to suggest that Thalia will bring great doom, and Percy takes it too literally, he could end up trying to kill her.
It could be that his siblings have made a pact with an extremely evil entity. Naruto, with his sense of justice and loyalty to the greater good, decides that their existence in that state is too dangerous and kills them, though it would be a very difficult and heart - wrenching decision for him.
Another reason could be related to a prophecy. There might be a prophecy that Boruto will bring great destruction in the future, and Naruto, as the Hokage, feels it's his duty to prevent this at all costs. He might think that by killing Boruto, he can change the course of fate and protect the people he loves and the entire ninja world.
It could also be due to a misunderstanding. Suppose Naruto accidentally does something that Kurama misinterprets as a threat to its own existence. For example, if Naruto tries a new jutsu that Kurama wrongly perceives as an attempt to suppress it further.