Another plot could involve Percy getting lost in a strange realm that is under the influence of the Joi Goddess. At first, he's confused and a bit scared, but as he gets to know the Joi Goddess, he discovers that she has been trying to protect this realm from an ancient evil that is starting to seep through the boundaries. Percy then decides to help her fight it off.
One idea could be Percy having to team up with the Joi Goddess to save Camp Half - Blood from a new, powerful enemy. Maybe this enemy has the ability to manipulate time and space, and only with the combined powers of Percy and the Joi Goddess can they figure out a way to stop it.
One idea could be that Percy discovers a hidden side of Goddess Lemon that no one else knows. Maybe she has a special power that only Percy can understand or help her control. Another could be that they go on a quest together, facing challenges that test their relationship and force them to rely on each other.
Percy's power over water could potentially combine with the Joi Goddess's power, which might be something like the power of joy or light. For example, Percy could create water constructs that are then infused with the positive energy of the Joi Goddess, making them more powerful and able to heal as well as fight.
Another interesting plot could involve Percy being hunted by both Greek and Norse monsters because he is an anomaly. He then has to team up with some unexpected allies, like a Norse dwarf and a Greek nymph, to fight back. As he does this, he uncovers secrets about his mother that change his whole perspective on his family.
Perhaps Percy discovers a hidden power within himself that is linked to the goddesses. This power attracts the goddesses to him, and they believe that by being in his harem, they can gain some advantage. However, Percy is initially hesitant as he is used to a more normal life. But as he gets to know the goddesses better, he starts to develop feelings for them, and they all have to figure out how to co - exist in this unusual relationship.
One plot idea could be Percy having to team up with Hera to rescue a group of demigods who have been captured by an ancient monster. Hera, despite her usual aloofness, realizes she needs Percy's unique skills.
One idea could be a crossover where Harry and Percy meet during a magical event that blurs the boundaries between their worlds. Maybe a powerful dark force is causing chaos in both the wizarding world and the demigod world, and they have to team up to stop it. They could share their unique magical abilities and learn from each other's fighting styles.
A great plot could involve Percy being sent on a quest by a primordial. Since primordials are so powerful and ancient, the quest would likely be extremely dangerous and full of unknown challenges. For example, he might have to retrieve an ancient artifact that was lost in the time before the gods. This could lead to Percy facing not only physical challenges but also moral dilemmas as he deals with the primordial's motives.
A plot could involve Hera taking Percy on a journey through the past to show him the origins of the gods' power and how it relates to the current problems in the demigod world. This would give Percy a new perspective and knowledge that he can use to save the day. Or perhaps Percy accidentally stumbles upon a secret of Hera's that she's been hiding for centuries, and she has to enlist his help to keep it safe, all while other gods are trying to uncover it too.
One idea could be Percy gets cursed by Circe to forget his friends and mission, and he has to struggle to regain his memories while under Circe's influence. Another could be Circe teams up with Percy to fight a common enemy that threatens both the mortal and magical worlds. Or perhaps Percy has to rescue his friends from Circe's island after they are turned into animals, but he discovers that Circe has a more complex backstory and motives than he thought.
A great plot could involve Percy going on a quest not for the typical reasons like saving the world or a camp, but to find a way to restore the memories of a friend who has lost them due to a powerful spell. Along the way, he discovers secrets about his own past that were hidden from him. He might also encounter new demigods with unique powers who either help or hinder his journey.