In the 'Percy Jackson' fanfiction where Artemis kills Percy, what could be the possible reasons for such a plot development?

It could be due to some external influence. Perhaps a powerful and evil force manipulates Artemis into thinking that Percy is a danger. This evil force might be using false evidence or illusions to deceive her. In the world of 'Percy Jackson', there are many such forces that could play such a devious role.

One possible reason could be a misinterpretation of a prophecy. Maybe Artemis believes Percy is a threat to the natural order she protects based on a wrongly interpreted prophecy. For example, if a prophecy was worded ambiguously and she thought Percy would bring destruction to the wild, she might take drastic action.

Another reason might be related to a conflict over power or territory. If Percy's actions were somehow seen as encroaching on Artemis' domain, like interfering with a sacred place of the wild that she is very protective of. His intentions might be good, but Artemis could misread them and see him as a threat to be eliminated.