Well, it could be that Percy's forgotten birthday is the final straw in his relationship with his family. He could decide to focus solely on his work at the Ministry, becoming even more of a workaholic. This would add to his already existing sense of alienation. Maybe he would meet someone at work who takes pity on him and tries to cheer him up, leading to an unexpected friendship.
To write an emotional plot for a Percy Weasley forgotten birthday fanfic, first focus on Percy's internal thoughts. Show his excitement building up to his birthday and then the crushing disappointment when it's forgotten. Use descriptive language to convey his feelings, like 'Percy's heart sank as the day passed without a single mention from his family.'
Well, he might go through the day feeling really sad and neglected. Maybe he'd see other people celebrating birthdays and it would make him feel even worse. He could start doubting his relationships with his friends and family.
Well, he might discover some ancient magic hidden within the pyramid. Maybe he'd encounter magical creatures that are specific to that pyramid environment. It could also be that he stumbles upon a prophecy or a powerful artifact that changes his perception of the wizarding world.
A Claptrap birthday fanfic could involve Claptrap getting a software upgrade as a birthday present. This upgrade could give him new abilities, like being able to sing happy birthday in multiple languages at once. And all the other characters would gather around, some reluctantly like Handsome Jack, but still there to celebrate. There could also be a big cake made out of some sort of Pandora - like substance, like eridium - flavored frosting.
One 'Percy Weasley forgotten fanfiction' that's quite good might be 'Percy's Redemption Arc'. It delves into Percy's journey of making amends after his falling - out with his family. Another could be 'Percy in the Shadows' which shows a side of Percy that was overlooked in the original series, his hidden talents and insecurities.
Perhaps the family could have a 'naked' themed photo booth at the birthday party. Everyone dresses up in funny, body - painted outfits that look like they are naked but are actually very creative and appropriate. They take pictures together and make a scrapbook for the birthday person.
In such a story, you might have guests arriving with funny presents, or someone could accidentally spill something and cause a little chaos. Also, the birthday person could make a touching speech.
In a fanfic, Percy Jackson might face some really tough opponents in the contest. He could use his water - controlling powers in creative ways, like making a huge water barrier to protect himself from attacks. Maybe he'd also team up with some unexpected allies he meets during the contest.
In this fanfic, Percy could be called upon to solve a mystery among the animals. Some animals are acting strangely and it seems like there's a curse. Percy uses his ability to understand the animals' language and his knowledge of magic to figure out the source of the problem. He might find out that an ancient artifact has been stolen and that's what's causing the chaos among the animals.
Well, it could be that Annabeth visits Percy to help him with some sort of problem. Maybe he's having trouble with his powers or there's a mystery at his place that she can assist in solving. They could have deep conversations about their past experiences and how those have shaped them into who they are now.