One idea could be that they face challenges in protecting their unborn child from dark forces in the Fairy Tail world. Maybe some old enemies resurface, seeing the baby as a threat or a powerful asset. Another could be the reactions of their friends in the guild. Some might be overly excited and constantly fussing over them, while others could be more reserved and worried about the future of the guild with Natsu and Lucy having a family.
Perhaps they discover that the baby has some unique magical abilities even before it's born. This could lead to a search for knowledge about these powers and how to control them. They could also go on a journey to find a safe place to raise the child, away from the chaos of their usual battles. And of course, there would be cute moments of Natsu trying to be a good father - like clumsily building a crib or talking to the baby bump.
A plot idea could be that a prophecy surrounds their unborn child. The prophecy states that the child will either bring great peace or great destruction to the world of Fairy Tail. This causes a lot of tension, not only within the guild but also among other magical groups. Natsu and Lucy then have to prove that they can raise the child to be a force for good. They would have to deal with the pressure and the added protection they need to give their baby.
One idea could be exploring how the other members of Fairy Tail support Lucy during her pregnancy. For example, Natsu might be overprotective, always making sure she's safe on missions or just in general. Another could be Lucy writing in her diary about her hopes and fears for the future as a mother, while also reflecting on her adventures in Fairy Tail.
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.
One plot idea could be how Lucy adjusts to her new state while still being part of the Fairy Tail guild. Maybe she has to take on less dangerous missions at first and her friends rally around to protect her. For example, Natsu could be overly protective, getting into comical situations as he tries to keep her out of harm's way.
Well, a plot could involve a new student arriving at Fairy Tail Academy who seems to have a connection to Natsu's past. Lucy gets a bit jealous at first, thinking there's more to it. As they all interact, they end up in a magical competition within the academy where they have to team up to face tough opponents. This not only tests their magical powers but also their friendship and loyalty to each other.
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.
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.
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.
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.
One plot idea could be that a magic spell goes wrong and Lucy ends up pregnant. Natsu is initially shocked but then quickly embraces the idea of being a father. They then have to deal with the guild's reactions, some of which are positive and some negative.
One idea could be that Natsu and Lucy are paired for a school project that involves exploring the magical history of their high school. Along the way, they discover a hidden room in the school that was once used by powerful mages in the past. This leads them on an adventure to unlock the secrets within and also brings them closer together as friends.