In a battle against a group of powerful enemies, Natsu overexerts himself and is on the verge of being defeated. Lucy steps in. She first summons all of her available Celestial Spirits to create a powerful defensive formation around Natsu. Then, she combines her own magical attacks with those of her spirits to drive the enemies away. After that, she uses her healing magic (if she has developed such in the fanfiction) to nurse Natsu back to health.
Well, Natsu might protect Lucy by using his dragon - like senses. In the Fairy Tail world, his enhanced senses can detect danger before it reaches Lucy. So, he could quickly react and pull her out of harm's way. Also, his loyalty to Lucy and the Fairy Tail guild drives him to protect her. He would not let any harm come to her, whether it's from other guilds who might have a grudge against Fairy Tail or from individual villains in the fanfiction. He'll be there to fight for her safety.
In the new Princess Huanzhu, the scene of Xiao Jian saving Qinger from falling into the water happened in episode 40. At that time, Qinger and Xiao Jian had escaped onto the boat while fighting with the experts. However, there were a few experts hiding under the boat. Their sudden appearance caused Qinger to fall into the water. Xiao Jian was very anxious, but he couldn't find Qinger, so he went into the water to search. In the end, he found Qinger injured. Xiao Jian urgently saved Qinger and used artificial resuscitation to wake her up. This scene showed Xiao Jian's concern and worry for Qinger.
In this kind of fanfiction, Natsu may also face challenges related to misinformation or deception. Enemies could trick him into believing that Lucy is safe when she's actually in danger, or vice versa. His emotions for Lucy can sometimes cloud his judgment as well. He might be so eager to protect her that he rushes into a situation without fully thinking it through. Additionally, there could be internal guild issues. For example, if some members of Fairy Tail have different ideas about how to protect Lucy or if there are rivalries within the guild that affect Natsu's ability to focus on protecting her. All these things can make it really hard for him to safeguard Lucy effectively.
In this kind of fanfiction, perhaps Itachi uses his quick reflexes and ninja skills to catch Sakura as she's about to fall. Maybe she was in a dangerous situation like on a crumbling cliff or a collapsing building. Itachi, being the powerful ninja he is, swoops in just in time to prevent her from getting hurt.
They can develop their relationship by having small, everyday moments. For example, sharing breakfast together as a family, where they talk about their plans for the day. Natsu could show his love for Lucy by being more protective of her and their family in dangerous situations. Also, they could have inside jokes that only their family understands, which would strengthen their bond.
One character that would be interesting to include is Mirajane. She has a motherly and observant nature. She could be the one to nudge Natsu and Lucy in the right direction when it comes to their relationship. For instance, she might arrange for them to go on a mission together that she knows will bring them closer. Laxus could also be in the fanfiction. His powerful presence can create a sense of danger or protection. If there's an outside threat to the guild while Natsu and Lucy are exploring their relationship, Laxus could be at the forefront of defending the guild, which would impact Natsu and Lucy's situation. And don't forget about Cana. She could be the one to create some light - hearted chaos, like daring Natsu and Lucy to do something that ends up bringing them closer, such as a bet that leads to a shared adventure.
As they travel, their bond deepens. They start to rely on each other more. Natsu becomes more protective of Lucy, and Lucy begins to understand Natsu's impulsive nature better.
A Natsu x Lucy pregnant fanfic could be full of heartwarming moments. Think about Natsu being overprotective of Lucy during her pregnancy. He'd probably be a bit clumsy at first, but his love for her would shine through. And Lucy would be the one trying to keep things in order while also dealing with her hormonal changes. It could also add a new dynamic to the Fairy Tail group as a whole.