Natsu might be initially shocked and confused. He's not the type to expect rejection, so he could be at a loss for words at first. For instance, he might just stand there with his mouth open, not believing what he just heard.
Natsu could handle the rejection by using it as motivation. He might train harder to prove himself to those who rejected him. For example, if he was rejected from a magic competition, he could practice new spells and techniques to show up the judges next time.
One possible scenario could be that Natsu confesses his love to a character, perhaps Lucy, and she rejects him because she doesn't see him in that way. She might think of him only as a good friend. Another scenario could be that Natsu is rejected in a job or a quest application within the fanfiction world. Maybe the guild he wants to join or the person in charge of a certain task doesn't believe he has the skills or the right attitude.
One possible reason could be that Erza is focused on her own goals and career in the Fairy Tail guild. She might see a relationship as a distraction at that moment. For example, she is always striving to be stronger and take on more challenging missions. Another reason could be that she may not view Natsu in a romantic way but more as a close friend and guildmate. Maybe she has a different ideal type in mind, someone more calm and studious rather than Natsu's brash and impulsive nature.
He could marry an original character created specifically for the fanfiction. This character could be a powerful mage from a far - off place who crosses paths with Natsu during one of his adventures.
One of the senior and more experienced members of the guild. They have seen a lot and know how things should be done in the guild. If Natsu acts in a way that goes against their long - established ways, they would not hesitate to berate him.
It could be Gray. Although they are friends most of the time, in a fanfiction, there could be a plot twist where Gray's envy of Natsu's abilities gets the better of him, and he betrays Natsu. Maybe Gray thinks that by getting rid of Natsu, he can be the top mage in their guild.
Well, in many fanfictions, Natsu might initially be in shock. He's a passionate character, so he could react with anger. He might lash out at Lisanna or the person she cheated with. He could also go into a state of self - doubt, wondering what he did wrong.
There could be such a fanfiction. Fanfiction writers often come up with all kinds of creative and sometimes out - of - the - box ideas. However, I haven't personally come across one where Natsu gets Erza pregnant. It might be a rather niche concept within the Fairy Tail fanfiction community, as most fanfictions tend to focus on different aspects of the characters' relationships, like friendship, adventure - related partnerships, or other forms of romantic development.