A possible main antagonist could be Kronos. He could be manipulating Ms. Dodds to turn against Percy. Since Kronos wants to destroy the Olympians, he might see Percy as a major threat and use Ms. Dodds' position in Percy's school to get closer to him.
One idea could be exploring Ms. Dodds' backstory before she became a Fury. Maybe she was once a normal teacher who got corrupted. Another could be Percy having to face Ms. Dodds in a different setting, like in the Underworld during a quest. And a third idea is that Ms. Dodds is actually not as evil as she seems and has a secret mission to protect Percy in a very strange way.
A powerful Titan who was previously imprisoned but has now escaped could be a great antagonist. This Titan could have a grudge against Percy for his role in previous battles and sees Mrs. O'Leary as a way to get to him. He could use his own dark magic to try and control Mrs. O'Leary or turn her against Percy.
Another plot could be that Mrs. O'Leary gets lost in the mortal world, and Percy has to find her. Along the way, he discovers that she has made some interesting mortal friends who are in danger because of her association with the demigod world. Percy then has to not only find Mrs. O'Leary but also protect her new friends from the monsters that are after them.
You can start by looking on fanfiction websites like Archive of Our Own (AO3) or FanFiction.net. Just search for 'Percy Jackson Mrs O'Leary' on their search bars and you'll likely find a variety of stories.
One idea could be that Mrs. O'Leary gets lost in the mortal world and Percy has to find her without using his demigod powers. It would be a fun adventure as he has to rely on his wits and the help of some mortal friends.
The Percy Jackson series was a series of fantasy novels written by Douglas Hofstadter, who told the story of the protagonist, Percy Jackson, and his adventures. The series included Defense Against the Dark Arts, The Magic Kingdom, Percy Jackson and the Sword of Fire, and Percy Jackson and the Curse of the Dragon.
The protagonist of the story, Percy Jackson, was a young magician who had a special ability--to communicate with dragons. In the series, Percy Jackson and his companions went on many adventures, their goal was to find lost magical treasures and fight against evil forces.
The plot of the series was full of fantasy elements and magic techniques, which was very popular among readers. At the same time, the characters in the novel also have their own characteristics, with profound character images and character descriptions, so that readers can understand and appreciate the story more deeply.
In Percy Jackson fanfiction, families can be depicted in various ways. Some might show Percy's family having new and unexpected adventures together. For example, his mom could discover a new magical ability that she uses to protect the family from an ancient threat. Another idea could be that Percy's half - brother Tyson becomes a key figure in protecting the family from monsters that target them specifically because of Percy's fame among the demigods.
One idea for a Percy Jackson famous singer fanfiction could be that a famous singer is actually a demigod in disguise. Maybe they use their music as a form of magic or to communicate with other demigods secretly. For example, their lyrics could hold hidden messages about upcoming quests or threats to the demigod community.