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.
Sasuke is a highly skilled ninja with incredible speed and combat abilities. If he was transported to the Harry Potter universe, he could use his physical prowess to protect Harry. For example, when Harry is being chased by Death Eaters, Sasuke could use his ninja techniques like the Chidori to fend them off. He could also use his Sharingan to read their movements and anticipate their attacks, thus saving Harry.
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.
Well, it might be that Harry Potter is accidentally transported to a non - magical realm where he is in trouble because he doesn't understand the Muggle world completely. The Queen, who has some knowledge of magic or is in contact with a secret magical society, discovers Harry and saves him from the perils of this strange new world for him.
It might be an ancient magical being that has the form of a queen. She could have ties to the very origins of magic in the Harry Potter universe and decides to save Harry because she foresees his importance in the future of magic. For example, she could be a guardian of some sort of magic that is crucial for Harry to defeat Voldemort in the long run.