Well, perhaps the story could start with Lucy finding out she's pregnant. Natsu is initially shocked but then becomes super excited. The pregnancy is filled with little adventures, like Natsu trying to build a perfect nursery using his magic in a rather clumsy way. And when the baby is born, it brings a new sense of hope and family to the whole guild. Everyone pitches in to take care of the baby, and it grows up surrounded by love and magic.
The plot might involve Natsu and Lucy facing challenges while raising their baby. For example, they might have to deal with an enemy who wants to use the baby for some evil purpose. The baby could also be a key to unlocking some long - forgotten magic in the world. Natsu and Lucy would have to balance their duties as parents with their roles in the guild. They would teach their baby about the importance of friendship and magic, and as the baby grows, it starts to show signs of being a great wizard in its own right, with a unique blend of Natsu and Lucy's personalities.
Well, perhaps in this fanfiction, Natsu calling Lucy 'baby' is a sign of a new level of closeness in their relationship. It could start with Natsu protecting Lucy in a dangerous situation and instinctively calling her 'baby' as he holds her close. This then leads to Lucy being a bit flustered at first but gradually getting used to it and even liking it, and it becomes a special part of their bond.
One possible plot could be that Natsu and Lucy accidentally end up taking care of a baby dragon. They struggle at first with things like feeding it and getting it to sleep. But as time goes on, they grow attached and learn a lot about themselves and their relationship in the process.
Maybe a rival guild that is jealous of Fairy Tail's new addition. They might think that having a baby with such strong magical potential in Fairy Tail gives them an unfair advantage. So they try to kidnap the baby to either keep it for themselves or use it to bargain with Fairy Tail.
One possibility could be that they discover they're having a baby unexpectedly. Natsu might be initially confused but then super excited. Lucy would probably be a bit more practical, thinking about how to raise the baby in the Fairy Tail guild environment. The guild members would be overjoyed and offer all kinds of help, like Happy bringing little gifts for the baby to be.
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.
The plot could involve the challenges they face as new parents. Maybe they struggle with balancing their own relationship while taking care of the baby. There could be financial difficulties or family interference that they have to deal with. And of course, there would be lots of cute moments like the baby's first steps or first words, which would bring them closer as a family.
One possible plot could be about the challenges they face as new parents. Maybe they have to balance their work with taking care of the baby. Gru, with his past of being a villain, might be worried about how his past could affect their child. Lucy, on the other hand, could be using her skills from the Anti - Villain League to keep the family safe. They might also have funny moments like when the Minions try to help with the baby but end up causing chaos.
One possibility is that the baby is a key to a mystery. Maybe it has some special power or mark, and villains are after it. Natsu and Lucy then take on the role of protectors, using their magic and friendship to keep the baby safe while trying to figure out its origin.
It could be a dark wizard who wants to use the baby's power for his own evil deeds. Maybe the baby has some special magic that the wizard thinks can help him take over the magical world.
The baby could inherit Natsu's dragon slayer magic. It might be able to breathe fire and have enhanced strength like Natsu. Also, from Lucy, it could have the ability to summon celestial spirits. Maybe it could even combine these powers in unique ways, like summoning a fire - breathing celestial spirit.