He could return with a whole new set of allies. During the war, he might have met other powerful mages who decided to follow him back to Fairy Tail. These new allies could bring different types of magic and skills to the guild. Also, Natsu might come back with a different perspective on life. The horrors of war could make him more determined to protect peace in the world and in his guild, leading him to take on a more leadership - like role in Fairy Tail.
Well, he could be magically healed by one of his friends. Maybe Lucy uses her celestial magic to call a spirit with healing powers.
The first thing that could happen is that his friends would immediately start to tend to his wounds. Erza, being the strong and reliable one, might take charge of the situation. She could use her medical knowledge, if she has any in the fanfiction world, or she could call for help from a more experienced healer. This would show the bond between Natsu and his friends.
After the kiss, it could be that they both realize their true feelings deeper. Natsu might start to see Juvia in a whole new light, not just as a friend. Juvia, on the other hand, would be even more in love. Their story could then develop into a series of sweet moments. For example, Natsu could start bringing her little gifts, like a flower he found on a mission. And they could start training together more often, which would strengthen their bond not only as a couple but also as stronger wizards.
Well, one possibility is that Yukino is completely taken aback. She might not be expecting it at all. She could initially say no because she's not sure about her feelings or she might be worried about how it will change their lives. But then, as she thinks more about it, she realizes that she does love Natsu and they start planning a future together.
One possibility is that Igneel would immediately go into a protective mode. He might use his dragon powers to heal Natsu if he has such abilities. Since they have a strong bond, Igneel would be enraged at whatever caused Natsu to get hurt and would seek revenge. He could also stay by Natsu's side until he recovers, providing warmth and comfort as dragons are often associated with being a source of strength and protection.
His friends would most likely try to heal him immediately. Wendy, with her Sky Dragon Slayer magic, could be the first to attempt to close his wounds and stop the bleeding. She has great healing abilities, so she would be crucial in this situation.
Natsu could develop a sense of guilt. If he lost comrades during the war, he might blame himself for not being strong enough. This guilt could either drive him to become stronger or make him more withdrawn. He may also start to question his own beliefs. For instance, if he had to do some morally ambiguous things during the war to win, he'll have to grapple with the consequences of those actions.
He might also have an emotional reaction. Spiderman is a very empathetic character. If the fanfiction shows some really tragic events during the Infinity War, he could be deeply affected. This could lead to him being more determined to prevent such tragedies from happening in his reality.
Hard to say for sure. Maybe there'll be unexpected alliances or powerful enemies emerging. Or perhaps the story will focus on character development and their internal struggles.
In the 'natsu went mia in war fanfiction', Natsu is presumably a central or important character. He could be a hero - type figure who was expected to play a significant role in the war. It's possible that he has some special abilities or traits that made his presence crucial. Since he went MIA, the whole story might be about his friends or allies trying to find him or dealing with the aftermath of his disappearance. It could also be that Natsu is a character with a complex backstory, and his going missing in action is a key event that will unfold and reveal more about his past, his relationships, and the overall world of the fanfiction.