Tethys could also be a candidate. Percy as the son of Tethys could have a connection to the oceans in a different way than his Poseidon - related powers. Maybe he could communicate with sea creatures on a deeper level or have the ability to control the tides in a more powerful way.
One idea could be Percy exploring his new powers that come from being the son of a Titaness. He might discover abilities that are different from his normal demigod powers and have to learn to control them quickly. For example, he could have the power to manipulate time on a small scale, like slowing it down in a battle to gain an advantage.
One common theme is the clash of two different worlds. Percy, from his heroic and somewhat mortal - associated world, and the titaness from a more ancient and powerful realm. Another theme is often about redemption or change, where the titaness might be on a path to change her ways because of Percy.
I'm not sure about a specific 'percy x titaness fanfiction' off the top of my head. However, you can try searching on fanfiction platforms like Archive of Our Own. There are usually a lot of unique takes on such pairings, and you might find one that suits your taste in terms of writing style and plot.
Love against all odds is a very prevalent theme. Given that Percy and the Titaness are not an ordinary couple, they face a lot of opposition. Their love has to overcome things like prejudice from others, differences in their upbringing, and the political implications of their relationship in the fictional world. Also, the theme of self - discovery is often there. Through their relationship, both Percy and the Titaness learn more about themselves.
Annabeth could be the mother. Since she and Percy have a strong relationship, it would be a natural choice. Their son would inherit both their intelligence and combat skills.
One popular 'Percy x Titaness fanfic' could be 'The Titaness's Choice'. It often explores the unique relationship between Percy and the Titaness in a world full of magic and adventure. The author does a great job of developing their characters and the plot is filled with twists and turns.
It could be Audrey, as she is Percy's wife in the original series. In fanfiction, they could have a more in - depth relationship story leading up to the birth of their son.
Frank Zhang could also be an ally. He is a Roman demigod with shape - shifting abilities. His strength and loyalty would make him a valuable teammate for Percy. Additionally, Nico di Angelo, who has ties to both the Greek and Roman worlds, could be an important ally. His knowledge of the Underworld and his ability to shadow - travel could help Percy in various situations, whether it's getting information or quickly moving around in the Roman camp.
Annabeth would definitely be one of his top allies. She's been with Percy through many adventures and her intelligence would be crucial in helping Percy understand his connection to the creator and any new situations that arise. For example, she could research ancient texts to find clues about the creator's intentions for Percy.
Nico di Angelo could be a great ally. Since he has his own connection to the Underworld, he might understand Percy's new situation better. Another could be Thalia, as she's always been a strong and loyal friend. She would likely stand by Percy despite his new dark powers. Also, Grover could be an ally. His empathy and loyalty would make him support Percy no matter what.