A really interesting plot might be a love triangle situation. Maybe Percy is in love with Katniss, but Katniss is involved with someone from her own world, like Gale or Peeta, and Percy has to compete in some way. This could add a lot of drama and tension to the story. Also, they could be in a post - apocalyptic world together, where they have to rely on each other's survival skills more than ever.
Another plot could be that they meet at a sort of inter - dimensional training camp. Here, they train other young heroes from different universes. But there's a mystery within the camp that they have to solve together. As they work together, they start to understand each other's cultures and values better, which could lead to a deeper connection between them.
A post - Hunger Games plot could be that Katniss and Prim are trying to help the children of District 12 who have been orphaned or traumatized. They start a small school or a healing center. Katniss teaches the kids survival skills, and Prim uses her medical knowledge to help them heal both physically and emotionally. This could also involve some challenges from the Capitol - loyal remnants in the district who don't want things to change.
Maybe the baby has some special abilities or characteristics that are unique to the world they live in. For example, the baby could have an uncanny ability to sense danger, like Katniss with her hunting skills. This would add an interesting dynamic as Katniss and Peeta have to figure out how to handle this while also being new parents.
A plot might involve a magical or sci - fi twist. For example, they get transported to a strange world where they have to solve puzzles and defeat monsters together. Along the way, their relationship deepens. Or perhaps there's a love potion mishap that makes them both have feelings for each other that they initially resist, leading to a lot of internal conflict and interesting character development.
One idea could be a what - if scenario where Katniss and Clove form an unlikely alliance in the arena. Maybe they realize that the Capitol is the real enemy and decide to team up against the other tributes. Another plot could involve Clove having a change of heart towards Katniss after seeing her kindness towards Rue. And a third idea is that they both survive the Hunger Games and have to deal with the aftermath together, facing the Capitol's wrath and trying to start a rebellion from within.
One idea could be that the baby is born during a time of unrest in Panem. Peeta and Katniss have to protect their child from the remaining threats. Maybe some old enemies resurface, and they use the baby as a target to get back at Peeta and Katniss.
Well, a plot could involve a spell gone wrong that merges the two universes. Harry and Katniss have to work together to undo the spell. Along the way, they learn about each other's worlds. Katniss could teach Harry how to hunt and survive in the wild, while Harry shows Katniss some basic magic for protection. And there could be a villain from both worlds who wants to keep the universes merged for their own evil purposes.
Another plot could be set during the Quarter Quell. Peeta and Katniss find out that there are some Capitol secrets hidden in the arena. They then team up not only to survive but also to expose these secrets. Their relationship would be put to the test as they face new and more dangerous threats.
One idea could be that Percy is framed for stealing a powerful magical artifact. His friends initially doubt him, but as he tries to prove his innocence, he uncovers a conspiracy within the magical community. For example, a secret group wants to use the situation to gain more power and is setting him up as a scapegoat.
One idea could be Percy getting involved in the Kurukshetra war. He might use his water - controlling abilities to change the course of battles near rivers or lakes. For example, he could create huge tidal waves to disrupt enemy formations.
One idea could be a time - travel plot where Percy goes back in time and meets a younger, different Medusa before she was turned into a monster. Another could be a story where Medusa somehow gets a chance at redemption and Percy has to decide whether to trust her or not. Maybe a plot where they have to team up to defeat a greater evil that threatens both of them.