It's a bit of a gray area. On one hand, fanfic is about creativity and exploring different ideas. But on the other hand, this goes against the established character relationships in the Percy Jackson series. So while some might find it an interesting and different take, others may be offended or think it's inappropriate.
In the Percy Jackson fandom, writing a 'Percy gets Thalia pregnant' fanfic is not really in line with the spirit of the original works. The relationships in the books are carefully crafted, and this idea is quite a deviation. But if the writer makes it clear that it's an alternate universe and not trying to rewrite the canon in a disrespectful way, it might be more acceptable. Still, it will likely be controversial among many fans.
This is a very unorthodox and non - canon idea. However, if such a fanfic were to exist, perhaps the plot could involve Percy and Thalia having to deal with the shock and the sudden change in their lives. They might face judgment from their friends and the demigod community. But this goes against the established relationships in the original works.
I really like 'Percy and Thalia's Adventure'. In this fanfic, they go on a quest together that was not part of the original books. The author does a wonderful job of capturing their personalities. Thalia's fierce and independent nature and Percy's loyalty are shown really well throughout the story.
One possible storyline could be the challenges Thalia faces while pregnant in a world full of mythological threats. She might have to rely on her friends more than ever. For example, Percy could be there to protect her from monsters that target her because of her condition. Another could be the emotional turmoil she goes through, as being pregnant might change her role in the group and her own self - perception. She could struggle with how this new situation affects her goals and dreams within the context of the Percy Jackson universe.
He could also offer emotional support. Percy could listen to Thalia's fears and concerns about the pregnancy. He might share his own experiences of dealing with difficult situations in the world of demigods, making her feel less alone. Maybe they could have long talks about how this will change their lives and what they need to do to prepare.
In the fanfic, it could be that Percy gets Triton as a gift from Poseidon. Triton could be initially reluctant to be with Percy, seeing him as an upstart half - blood. But as they spend time together, they start to understand each other better. Triton might help Percy improve his control over water, especially in more complex and powerful ways. They could go on quests together, like finding a lost ancient sea artifact that has the power to either save or destroy the world of the sea gods.
These fanfics can have a significant impact. They add new dimensions to the characters. For Percy, being sick shows his vulnerability, which is not always explored in the original books. It makes him more relatable to fans who have also experienced illness. Fans can then engage more deeply with the character.
Adventure themes are very common and great. For example, Percy going on new quests in the world of Greek mythology, facing unknown monsters and challenges. Another good theme is the development of relationships, like the deepening of his friendship with other characters or a budding romance.
There's also 'Percy and Thalia: The Hidden Past'. This one uncovers some secrets from their past that they didn't even know about themselves. It's a long read but well worth it as it adds a whole new layer to their relationship.
There's a fanfic called 'Thalia and Percy's Adventures Beyond Camp'. In this one, they team up to go on a quest outside of Camp Half - Blood. The author does a wonderful job of capturing their personalities. Thalia's tough and independent nature combined with Percy's loyalty and humor makes for an engaging read. The story also features some interesting new mythological creatures that they have to face together.
There shouldn't be any legitimate fanfiction with such a plot. The Percy Jackson series has a certain set of rules and moral and ethical boundaries within its fictional universe. The idea of Percy getting Hera pregnant is not only out of character but also violates the general tone and values of the series.