Perhaps he has been exposed to some sort of deadly and unknown substance in the mythical world. This could be a new type of monster venom or a strange plant that he accidentally ingested. The substance could be attacking his body from the inside, causing his internal organs to bleed, and thus he throws up blood.
Grover would be panicked. He's Percy's friend and he cares a great deal about him. He might start running around trying to find help, like looking for a healer or someone with magical healing abilities. He'd probably be muttering to himself about how he should have protected Percy better.
It could be related to a new and strange power he's trying to control. Percy is constantly evolving and getting new powers. If he tries to tap into a power that his body isn't ready for, it might have some adverse physical effects like vomiting. Like when he first started to understand his water - based powers, there could be something similar but more extreme with a new power.
It can create a sense of urgency. If Percy throws up, it might mean he's been poisoned or is seriously ill, and his friends will have to find a way to help him quickly. This can drive the plot forward as they search for a cure or a way to make him better.
Try this one: 'Are you a demigod? Because you've got the power to make my heart race faster than a satyr at a party.' Satyrs in the series are known for their energetic and wild nature, so comparing the effect the person has on your heart to a satyr's energy is a fun way to flirt. It also ties in the concept of demigods which is central to the Percy Jackson world.
It could be a rogue demigod who wants the throwing stars for their power. This demigod might have been shunned by the other demigods and sees the stars as a way to gain revenge and power over them.
Perhaps the throwing stars are cursed. Percy's guardian unknowingly passes them on to him. Percy starts having strange dreams related to the stars' origin. He has to find a way to break the curse before the stars turn him into a weapon of the dark forces. Along the way, he teams up with some of his demigod friends who help him research the history of the throwing stars and find a solution.
Well, a great plot for a Percy Jackson Camp Half - Blood fanfic could be a time - travel story. Imagine some of the demigods being sent back in time to the era when the gods first created Camp Half - Blood. They could witness the founding events and also face the challenges that the first demigods had to endure. Or perhaps a story where the camp is invaded by a group of demigods from another pantheon, like the Norse demigods. This would lead to a lot of clashes and also potential alliances as they try to figure out who has the right to be at Camp Half - Blood. Also, a plot where a demigod discovers they have a connection to a long - lost prophecy that could change the fate of the camp forever.
There are indeed some great ones. The 'bad boy' aspect often adds a new dimension to Percy's character. In some fanfics, he might be rebellious in a different way compared to his canon self, getting into all sorts of adventures and challenges at Camp Half - Blood that are not in the original books. You could also try looking on Wattpad, as there are many Percy Jackson fanfics there too.