Well, perhaps in this fanfic, the Goblin Academy has some sort of problem that only Harry can solve. He joins to help them out, and along the way, he makes new friends among the goblin students. He might also learn about goblin history and magic that is different from what he knows at Hogwarts.
In this fanfic, it could be that Harry is invited to the Goblin Academy of Youth due to his reputation as a powerful wizard. Once there, he has to deal with the politics within the academy. There might be different factions among the goblins, and Harry has to navigate through them while also trying to improve his own magical skills in the goblin - style magic. He may encounter some ancient goblin magic that is far more complex and different from what he's used to, and his presence might stir up some old rivalries or create new alliances within the academy.
It could be a jealous goblin student who doesn't like an outsider like Harry coming into their academy and stealing the spotlight.
Perhaps in this fanfic, Naruto joins Kuoh Academy because he's on a mission to learn about a strange new power that has been detected there. Once he arrives, he finds that the students have their own unique abilities, like the devils in the original Kuoh Academy setting. Naruto has to navigate between his ninja code and the new set of rules at the academy. He might end up teaching the students some of his ninja techniques while also learning from them about their powers, leading to a cross - over of skills and cultures within the academy.
Well, one possibility could be that Harry, through some sort of magical accident or powerful spell, gets transported to the world of Loki. Maybe he initially mistakes Loki for a powerful wizard and tries to seek his help to get back home. Loki, being the trickster he is, might see Harry as an interesting pawn in his schemes against the Asgardians or other foes. Harry, with his own magical skills from the wizarding world, could end up being both a hindrance and a help to Loki, leading to all sorts of adventures and misadventures as they navigate their two very different magical realms.
One possibility is that Harry joins SHIELD after realizing the magical world can't fully contain the threats he's faced. In the fanfic, he could be a key figure in bridging the gap between the magical and non - magical worlds within SHIELD. He might introduce magic - based security measures or use his ability to detect dark magic to identify threats that normal technology can't pick up.
In the 'harry joins voldemort fanfic', it could start with Harry being captured by Voldemort. Instead of killing him immediately, Voldemort decides to brainwash him. Through a series of dark magic spells and psychological manipulation, Harry starts to see Voldemort as a mentor. As time passes, Harry becomes an integral part of Voldemort's inner circle, helping him plan attacks against the wizarding world, believing that they are actually for a greater good as Voldemort has convinced him.
Well, perhaps Harry could discover a magical portal that leads him to the Protoss world. There, he might learn their advanced technology and unique culture. Maybe he uses his magic in combination with Protoss powers to fight off some common enemies.
One possible plot for 'harry joins the military fanfic' is that Harry joins the military to find a new purpose in life. He comes from a troubled background and sees the military as a way to discipline himself. He starts in a basic training unit where he meets all kinds of different people from different walks of life. As he progresses, he discovers a hidden conspiracy within the military that threatens national security. Harry then uses his wits and new - found military skills to try and expose the conspiracy and save the day.
The plot could involve Harry using his magic in the Stargate universe. Maybe he could use spells to help the Stargate teams in their battles against the Goa'uld. For example, a simple Stunning Spell could be very useful against the Jaffa warriors. He could also use magic to decipher some of the ancient technologies that the Stargate teams come across, since he has experience with ancient magic in his own world.
One possible plot could be that Harry is brought into the SG1 world because of a magical accident involving the Stargate. Once there, he realizes that there are dark forces at work in this universe too. He teams up with SG1 to find a way to get back home while also helping them to stop an impending invasion. Harry uses his Patronus charm to fend off some of the scarier alien creatures, and his knowledge of potions comes in handy when they need to cure a strange alien disease.
The plot might revolve around Harry's adaptation to the military lifestyle. He'd have to get used to the strict discipline, early mornings, and intense physical training. Along the way, he might discover a hidden talent for air combat strategy. And there could be a sub - plot about his relationship with his family back home who are both proud and worried about him.