There's also a chance it's a member of a rival guild who wants to take out Fairy Tail's strongest member to gain an advantage in some sort of guild competition. It might be a strategic move on their part.
Or perhaps it's an assassin hired by an unknown enemy. This enemy could be someone who is afraid of Natsu's power and wants to eliminate him before he becomes even more of a threat.
It could be a dark wizard who has a vendetta against Fairy Tail. Maybe someone who Natsu defeated in the past and is now seeking revenge.
It could be a jealous rival detective who wants to get rid of Sherlock to gain more fame in the detective world.
It could be a new villain who has a vendetta against Tony. Maybe this villain has some past connection to Tony that we don't know about yet, and they finally take their chance to harm him by shooting him.
It could be a former criminal that McGee helped put away. They might have escaped from prison and are seeking revenge on him for ruining their life.
There's also a possibility that it's someone who has a wrong idea about Conan. For example, a person who thinks Conan is involved in some sort of conspiracy against them or their family. This misunderstanding could lead them to shoot Conan in a moment of rage or fear, without really knowing who Conan truly is and what he stands for.
There's also a possibility that it's an agent of a secret organization. This organization might be aiming to disrupt the hero society, and they see Bakugou as a key figure to target. So they send one of their best shooters to take him down.
It could be a new villain, someone who has a personal vendetta against Peter Parker. Maybe a criminal whose operations Spider - Man has disrupted one too many times.
Maybe it's a rival agent who is jealous of Booth's success and popularity within the agency. They might see shooting Booth as a way to get ahead in their career or gain more power within the organization.
It could be Nathan Prescott. He has a history of being unstable and involved in some dark things in the game. Maybe he has finally snapped completely and decides to target Max for some reason, perhaps because he feels she's getting in the way of his family's plans or because he blames her for his own problems. Another possibility is that it could be someone from the other side of the Arcadia Bay conflict, like a person who doesn't want the lighthouse to be saved and sees Max as the main obstacle to their plans.
Well, he could be magically healed by one of his friends. Maybe Lucy uses her celestial magic to call a spirit with healing powers.
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.