Who could be the one to hand Vance's ass to him in NCIS fanfiction?

It could be Gibbs. Gibbs is known for his no - nonsense attitude. If Vance made a decision that went against Gibbs' principles or the best interests of the team, Gibbs might be the one to give him a hard time.

Maybe he gets outsmarted by a new villain in the story. This could lead to him being in a really tough situation, like getting captured or making a big mistake that puts the whole team at risk.

Well, it could be due to a failed mission under his leadership. Maybe he made a wrong call during an operation and it led to bad consequences for the team. And his superiors or colleagues might not be happy about it, thus he 'gets his ass handed to him'.

Master Hand could be an ancient being that has been observing the Naruto universe from afar. Maybe he's a sort of guardian of the balance between different worlds, and when Naruto's situation threatens to disrupt that balance, he steps in.

It could be an old enemy of the NCIS LA team. Maybe someone they put behind bars before who has a vendetta against them and specifically targets Kensi as she's a key member. Or it could be a rival agency trying to get some inside information from her by kidnapping and interrogating her.

It could be his own mother. She might realize that he has become too dangerous and, in a moment of heart - breaking decision, find a way to destroy him. Maybe she discovers a weakness and uses it against him, driven by her love for humanity and the knowledge of the destruction he could cause.

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.

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.

One motivation could be revenge. Maybe someone from her past in Mossad or a past case she worked on in NCIS has a grudge against her and wants to make her suffer. Another motivation could be that she has some valuable information that a bad guy wants to get out of her, like details about a secret operation or the identity of an undercover agent.

'Him' could be a centaur. In the Harry Potter universe, centaurs are intelligent and powerful beings. Harry might ride a centaur in a situation where he needs to quickly cross the forest and the centaur's speed and knowledge of the terrain would be very useful.