The Titans could still be a major threat. For example, Kronos' followers who might be trying to rise again and regain power. They could target the children of Athena because of their wisdom and strategic abilities, seeing them as a big obstacle to their plans.
Well, a possible storyline is Percy dealing with the expectations of the camps of Apollo and Athena. Since he's the son of both in this fanfiction, he might be pressured to be the best in both areas like archery and battle strategy. He could also go on a quest where he has to use his Apollo - given musical talent to charm a dangerous monster and then use Athena - taught wisdom to outwit another foe.
Another plot could involve Percy having to prove himself to the children of Athena. Since he's not a child of Athena, they might be skeptical of his abilities at first. But as they face challenges together, like deciphering ancient prophecies that are hidden in Athena - related temples, Percy shows his worth through his quick thinking and battle skills. This could lead to a great friendship and mutual respect among them.
Percy would likely become more studious. Since Athena values knowledge, he would be more interested in learning about history, magic, and other aspects of the demigod world. He might spend more time in the library at Camp Half - Blood, much to the surprise of his friends. His relationships with others would also change. He could be more aloof at first as he tries to adapt to his new role, but as he grows into it, he would form deeper, more intellectual connections with those around him.
Another plot could involve Percy getting a vision from Athena about a future threat to the demigod world. But the vision is so cryptic that he has to work closely with Athena to decipher it. Along the way, they build an unexpected bond, different from his usual relationships with other gods. Maybe Percy starts to see Athena not just as a powerful deity but as a mentor figure, and Athena starts to respect Percy's tenacity more than she expected.
One great Percy Jackson and Athena fanfiction is 'Athena's Champion'. It really delves into the relationship between Percy and Athena in a unique way. The author portrays Athena as having a more hands - on role in Percy's adventures, guiding him with her wisdom in ways that are not explored in the original series.
One idea could be a story where Percy teams up with the Athena Hunters on a quest. Maybe they are searching for a lost artifact that has the power to change the balance between the gods. Percy's water powers could complement the skills and knowledge of the Athena Hunters.
One idea could be Percy struggling to fit in with Athena's children at first. Since he's used to being a son of Poseidon, he has different ways of thinking and acting. Another plot could involve him using his newfound Athena - given wisdom to solve a really complex mystery in the demigod world. Maybe he discovers a new prophecy related to Athena that only he can understand because of his unique position as her adopted son.
Another theme is the exploration of power and wisdom. Since Athena is the goddess of wisdom, fanfictions usually explore how Percy can benefit from her wisdom and how his own power combines with it. For example, in some fanfictions, Percy's combat skills are enhanced by Athena's strategic advice. Also, the theme of trust is often present. Given their different natures, Percy and Athena have to build trust in order to work together effectively in the fanfiction stories.
One common theme is the exploration of wisdom. Since Athena is the goddess of wisdom, many fanfictions show Percy learning from her, like how to think more strategically in battles. For example, in some stories, Percy starts to analyze his opponents' weaknesses before attacking, which is a very Athena - like approach.