It could be that Artemis betrays female Percy out of a sense of duty to the gods' code. Suppose there is a rule among the gods that female Percy has unknowingly broken. Artemis, being a strict adherent to the gods' laws, decides to take action against her. This could involve setting traps or leading her into dangerous situations, all in the name of upholding the divine order.
Well, she could betray Percy by revealing his secrets to his enemies. Maybe she's forced to do so under some kind of magical compulsion or threat.
Well, perhaps in this fanfiction, Artemis betrays Percy for Orion due to a prophecy. There could be a prophecy that states that Orion and Artemis together will bring about some great change or prevent a huge disaster, and Artemis believes she has to choose Orion over Percy to fulfill it. Also, Orion might have some sort of leverage over Artemis that forces her to turn her back on Percy.
Percy could lose trust in the gods completely. After Artemis' betrayal, he might feel that he can't rely on any of them anymore.
In this fanfiction, perhaps Percy is influenced by some dark force. This force convinces him that the Olympians are corrupt and need to be overthrown. He then betrays them by stealing important artifacts from Olympus that are crucial for its protection. He might also try to turn the demigods against the Olympians.
Some fans might be really shocked. They are used to seeing Artemis as a more or less benevolent figure, so this sudden betrayal would be a big twist. They'd probably be eager to read more to find out the reasons behind it.
Initially, Percy is likely to be heartbroken. He thought he had a certain relationship with Artemis, whether it was friendship or respect. So when she betrays him for Orion, he may go into a state of self - doubt. He could wonder what he did wrong and start to isolate himself. But as time passes, he may gather his strength and decide to face Artemis and Orion head - on, to either regain Artemis's trust or show her the error of her ways.
One possible plot could be that Artemis is captured by some powerful ancient enemy, like a primordial being. Percy, with his skills and courage, embarks on a quest to find her. He might face various challenges and monsters along the way. Maybe he has to solve some riddles related to the moon, as it's Artemis's domain. Finally, he locates Artemis and uses his water powers in a creative way to defeat the captor and free her.
One possible plot could be Percy getting caught in one of Artemis' hunts by accident. They initially clash due to their different natures but gradually develop feelings for each other.
One possibility is that Artemis has been misinformed. Some enemy of Percy has tricked her into thinking that Percy is a danger to the demigods. So she kidnaps him to stop him from causing harm. But as she keeps Percy captive, she slowly realizes that she has been deceived when Percy starts to explain his side of the story and the real threats he has been fighting against.
A plot could be that there's some sort of dark magic that is affecting the balance between the gods and the demigods. Artemis and Percy are brought together to combat it. Along the way, Percy shows a side of himself that Artemis is drawn to. His courage and selflessness intrigue her. And in a moment of vulnerability, Artemis kisses Percy. This kiss then becomes a catalyst for a deeper exploration of their relationship and the greater threat at hand.