Her power could be related to healing. Since the demigods often get injured in their battles and adventures, having a healer in the family would be a great advantage. She could use her power to heal not only Percy but also other demigods. This would make her very popular in the camp and also attract the attention of the gods. Some gods might want to use her for their own purposes, while others might want to protect her because of her valuable gift.
In Percy Jackson fanfics, his powers are often enhanced and explored in creative ways. His ability to control water can be shown in more extreme situations, like creating massive tidal waves to protect his friends or using water currents to travel at super - fast speeds across the ocean.
In fanfiction, Percy Jackson's lightning powers often get enhanced or modified in interesting ways. Some authors might have him control lightning in more precise forms, like creating lightning cages to trap enemies. It adds a new level of coolness to his already amazing abilities.
Percy's ability to communicate with sea creatures could prove useful in Hermione's world too. He could ask the mermaids in the Hogwarts lake for information, and Hermione could use her magic to translate if there are any language barriers. And on the other hand, Hermione's magic could help Percy when he's in a situation where his demigod powers alone aren't enough. For example, she could use a spell to make him invisible when he needs to sneak around in a place where his powers might be detected.
His power over water could also be used in a more spiritual way. He could communicate with the water spirits and ask them for help in healing Artemis. The water spirits might then infuse the water Percy uses with their own magic, making it more potent for healing. Percy could then use this enchanted water to heal Artemis' internal injuries as well as external ones.
In a Percy Jackson baby sister fanfic, she could have some really cool adventures. Maybe she discovers she has her own unique powers early on, like being able to communicate with sea creatures in a different way than Percy. She could also get into trouble by wandering into the wrong part of the camp, like the restricted areas where the more dangerous magical items are kept.
Perhaps she's a sister who was thought to be dead but actually survived. She could have been corrupted by the experiences she had while being 'dead'. When she returns, she blames Percy for not saving her properly. This false blame leads her to betray Percy. She could start spreading rumors about Percy being a coward or a bad leader among the demigod community.
In Percy Jackson fanfiction, his fire powers can be a really cool addition. Sometimes, authors might give him these powers as a new aspect of his godly heritage. Maybe he gets it from a previously unknown godly ancestor related to fire. It could also be a result of some sort of magical encounter or a unique curse that turns into a power.
In fanfiction, Percy Jackson's powerful water powers can be depicted in various ways. Some might show him creating massive tidal waves to defend against powerful foes. For example, he could use his powers to flood an entire battlefield, leaving his enemies struggling to stay afloat while he and his allies remain in control. This showcases the sheer scale of his water - based abilities.
Give her a distinct personality. For example, she could be really curious, always asking questions about the demigod world. Make her brave but also a bit naive at times. She might be more in tune with nature than other characters, able to sense things about the environment. Another aspect is to show her relationship with Percy. She could look up to him and want to be just like him, but also have her own ideas about how to handle situations.
Percy's powers would be a great addition to the Avengers in a fanfiction. His control over water could create a lot of strategic opportunities. He could flood an area to slow down enemies or create ice platforms for the Avengers to stand on during battles. Compared to Captain America's leadership and combat skills, Percy could offer a different kind of support. And when it comes to Thor, while Thor controls lightning, Percy could use water to conduct that lightning in different ways for more powerful attacks.