Maybe it's a new villain that has a grudge against the whole group. This villain could be after some power that Percy's guardian possesses, so they try to harm the guardian to get it. They could be a dark sorcerer or a corrupted demigod.
It could be an old enemy of Percy's, like a vengeful god or a powerful monster. They might be targeting Percy's guardian to get back at Percy.
There's also the possibility that it's a group of antagonists. For instance, a band of thieves or a cult that believes in some dark prophecy related to Percy's guardian. They would stop at nothing to get to the guardian and Percy and Thalia have to fend them all off.
The fanfiction could revolve around the relationship between Percy and Thalia as they work to safeguard Percy's guardian. It could show how their friendship or partnership develops during the course of their adventure. For example, they could start off not getting along so well, but as they face challenges, they learn to trust and rely on each other more.
In some fanfictions, it could be an ancient and powerful Titan who has escaped from Tartarus and is seeking revenge on the demigods. This Titan might see Percy and Thalia as the main obstacles in his path to domination.
A powerful Titan who has escaped from Tartarus could be the main antagonist. He might be seeking revenge on Artemis for her role in the previous battles against the Titans. This Titan could have new and terrifying powers that make him a formidable foe for Percy and Artemis.
A possible main antagonist could be a rogue demigod who was once rejected by the Hunt and now wants revenge. This demigod could have allied with some powerful monsters and is constantly causing trouble for the Hunt. For example, they might be stealing important artifacts or sabotaging the Hunt's missions.
A powerful Titan who was banished to the moon in the past and now wants revenge on the gods by destroying the moon could be the main antagonist.
It could be a powerful demigod who has been corrupted by greed. He wants to use the power of the earth for his own gain, like creating his own kingdom or something. So he's trying to stop Percy from protecting the earth because Percy stands in his way.
It could be an ancient and vengeful Titan who was once imprisoned by the Hunters' predecessors. Now free, it wants to destroy the Hunters to regain its lost power and take revenge on those who once locked it away.
The main characters are Percy and Thalia. Percy is often known for his bravery and quick thinking in various situations. Thalia, on the other hand, has her own set of unique abilities and a strong personality. In the context of the 'Crying Guardian' fanfiction, they both take on the role of protectors with a special connection related to their crying, which might be a source of power or a symbol of their deep emotional bond.
A major reason could be the loss of someone they were supposed to protect. If a young demigod under their care dies, they would feel an intense sense of guilt and failure, which could lead to crying.
One great 'Percy Jackson Guardian Thalia Fanfiction' is 'Thalia's New Quest'. It shows Thalia in a whole new adventure, facing challenges that really test her skills as a guardian. The author does a great job of portraying her strong and independent nature.