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.
Perhaps it's a new villain who has a grudge against NCIS as a whole and sees McGee as an easy target to send a message. They might be part of a criminal organization that NCIS has been investigating recently, and shooting McGee is their way of trying to derail the investigation.
There's also a chance that it's someone within NCIS who has some sort of hidden agenda. Maybe they're jealous of McGee's success or they're being blackmailed into doing it. This would add a lot of drama and mystery to the fanfiction as his friends try to figure out who among them could be the shooter.
Well, one possibility is that his team members go into a full - on investigation mode to find out who shot him. They might follow some leads that initially seem promising but turn out to be dead - ends. Meanwhile, McGee could be in a critical condition in the hospital, with his life hanging by a thread, and his friends are all worried sick about him.
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 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 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.
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.
Well, perhaps a new character introduced in the fanfiction. Maybe a spy from a rival agency who sees Abby as a threat to their mission. Or it could be an associate of a major criminal that the NCIS has been investigating. They might think that by shooting Abby, they can disrupt the investigation. Also, it's possible that it's a person with a personal vendetta against Abby, like someone she unknowingly wronged in the past.
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.