One possible plot could be that Natsu and Lucy meet in a completely new and unexpected place, like a parallel magical world. They have to rely on each other to find their way back home while also uncovering the secrets of this strange new world.
Perhaps they meet when they are both on a secret mission. Lucy is on a quest for a rare celestial spirit item, and Natsu accidentally stumbles upon her. They then decide to team up as they realize their goals might be related in some way. Natsu's brute strength and Lucy's strategic thinking could make for an exciting adventure together.
One idea could be that Natsu and Lucy face challenges in their guild duties while being pregnant. They might have to balance protecting the guild and their unborn child. For example, they could go on a mission that seems easy at first but turns out to be more dangerous due to Lucy's condition, and Natsu has to be extra cautious to protect her.
A plot idea could be that an old enemy from Natsu's past returns and targets Lucy to get to Natsu. Natsu then has to go all out to protect Lucy, and in the process, they both learn more about each other's fears and insecurities. Or perhaps there is a magical competition in which Lucy and Natsu team up, and they face various challenges that test not only their magical abilities but also their friendship and trust in each other.
In 'natsu x lucy family fanfiction', an interesting plot could be that Natsu and Lucy's family discovers an ancient prophecy related to their family line. The prophecy foretells that their family will play a crucial role in saving the magical world from a great evil. As they try to understand the prophecy, they encounter various challenges. Their family might have to travel to different parts of the magical world, meet new allies and enemies. Also, the kids in the family could start to show unexpected powers as they grow up, which adds more to the family's journey in fulfilling the prophecy.
Well, in many such fanfictions, it often involves Natsu and Lucy having a special connection related to dragons. Maybe Natsu's dragon powers play a role in bringing them closer in a romantic or fated - mates - like way. For example, they might go on adventures together where Natsu's dragon instincts protect Lucy in a more profound way than in the original story, and their relationship deepens as they face various challenges side by side.
I'm not sure specifically as I haven't read this particular fanfiction. But generally, it might involve Natsu and Lucy having some sort of adventure or interaction at a lemon spa. Maybe they go there to relax after a tough mission and something unexpected occurs during their time at the spa.
Perhaps Natsu kidnaps Lucy as a prank that goes wrong. He initially thinks it'll be a funny joke, like taking her away during a guild party just for a bit of chaos. But then things get out of hand. Lucy might be really angry at first, but as they are alone together, they start to have some deep conversations and understand each other better.
Maybe the guild holds a special event where everyone has to swap roles, and Lucy ends up as a maid. Natsu, being his usual self, follows her around, getting into all sorts of comical situations as he tries to help her with her maid duties. For example, he might accidentally set something on fire while she's trying to clean, and they have to work together to fix it.
One idea could be that Natsu and Lucy accidentally end up taking care of a baby dragon. Natsu would be excited to teach it fire - breathing tricks while Lucy would be more focused on keeping it safe and fed. Another plot could involve a magic spell gone wrong that turns them into babies themselves, and they have to figure out how to reverse it while in this state. It could also be a story where they find a lost baby in the forest during one of their quests, and they decide to raise it together, which would show their growth as characters in terms of responsibility.
A fun plot could be that a magical creature gets into the shower with them. It's a small, mischievous thing that likes warm water. Natsu tries to catch it while Lucy tries to calm it down, leading to a lot of chaos and laughter.
A great plot could involve Natsu and Lucy adopting a child with no magic. They would teach the child how to be strong in other ways and how to face challenges without relying on magic. The family could then get involved in a mystery that is related to the child's past. As they dig deeper, they discover secrets that not only help the child understand their origins but also put the whole family in danger. It would be a story about family, love, and facing the unknown.