It might be that the NCIS is called in due to some strange happenings in the wizarding world that are also affecting the Muggle world. They start investigating and realize that Harry Potter is a key target. They then use their resources, like their high - tech surveillance equipment and their well - trained agents, to protect Harry. They could set up a perimeter around Hogwarts or wherever Harry is, and fend off any attackers, saving him in the process.
In fanfiction, it could be that the NCIS has some sort of magical knowledge or artifacts. Maybe they've been dealing with cases that are on the fringes of the wizarding world without realizing it. When they discover that Harry Potter is in danger, they use this knowledge or these artifacts to save him. For instance, they could have an ancient amulet that can counter dark magic spells aimed at Harry.
In some fanfictions, Harry might be saved by NCIS through their excellent investigative skills. They could uncover a plot against Harry in time, using their resources to track down the bad guys before any harm comes to Harry.
Another possibility is that there is some sort of crossover magic. Maybe a spell goes wrong and links the NCIS world to the Harry Potter world. The NCIS agents, being the resourceful people they are, quickly adapt to the situation. They learn about the danger Harry is in, perhaps from Hermione who has some knowledge of both worlds now. Then they use their own brand of justice and skills to save Harry from whatever dark forces are after him.
In this fanfiction, perhaps Harry Potter is brought into NCIS because there are rumors of a wizard - made weapon being used in crimes. He would have to navigate the non - magical world of law enforcement while also keeping his own magical identity a secret. His owl, Hedwig, could be used to send messages in a discreet way that NCIS could benefit from. He might also introduce some of his wizard friends, like Hermione, to help with research using magic - enhanced techniques.
One common scenario could be Harry being framed for a crime he didn't commit. NCIS steps in to investigate and realizes the truth, thus saving Harry from unjust imprisonment.
One possible plot could be that Harry Potter uses his magical skills to solve a case that NCIS is stumped on. For example, he could use the spell 'Revelio' to find hidden evidence that normal forensic techniques couldn't detect. His knowledge of the wizarding world might also lead him to suspect that a suspect is using some form of dark magic or enchanted object in their crimes.
In fanfiction, Harry Potter as an NCIS agent might use his magical skills in unique ways. For example, he could use a spell to quickly analyze evidence that would otherwise take hours for normal agents. His ability to sense danger, developed from his years fighting Voldemort, would make him excellent at detecting threats on the job.
It could occur during a time when Harry is on the run from Voldemort. Mary Poppins, being in the right place at the right time, might see Harry in distress. She could then use her magic to create a diversion or shield Harry from Voldemort's attacks. Since Mary Poppins has the ability to enter and exit different realms quite easily, she could whisk Harry away to a safe place, perhaps even a place outside of both the wizarding and Muggle worlds where Voldemort couldn't reach him.
One possibility could be that Voldemort has a sudden change of heart. Maybe he realizes that Harry is the only one who can truly understand his loneliness and power. So instead of killing Harry, he decides to save him from a dangerous situation, like a powerful dark magic that even Voldemort fears could destroy the wizarding world if not controlled, and in the process, they form an unlikely alliance.
In the 'Harry Potter Saved by Demons' fanfiction, perhaps the demons are not as evil as they seem in the traditional sense. They might be outcasts from their own demon realm. When they come across Harry, they recognize his power and the danger he's in. They decide to save him because they believe that by doing so, they can change the fate of both the wizarding world and their own world. So they use their unique demon abilities to keep Harry safe from harm.
Well, perhaps the Winchesters, who are known for hunting supernatural beings in their own universe, find a way into the Harry Potter world. Maybe they sense some dark magic that the wizards in Harry Potter's world can't handle on their own. They then use their skills and knowledge of the supernatural to save Harry from a powerful dark wizard or a dangerous magical creature.