It could also be that Harry is smart about people and relationships but doesn't show it. He might be able to read others really well and manipulate situations subtly. For instance, he could be using his knowledge of how different characters interact and what they want to further his own goals, like getting the support of certain Hogwarts houses or influential wizards, all while appearing to be just a normal, not - overly - smart student.
Perhaps in the fanfic, Harry is smart in ways that are not recognized by the wizarding world's traditional measures. He might have an in - depth understanding of magic that goes beyond what he shows in school. Maybe he's secretly researching ancient spells and magic theories that could be used to solve bigger problems in the wizarding community, but he doesn't want to draw attention to himself until he's fully prepared.
Ron could also be in it. He might initially not believe that Harry is hiding his intelligence, but as the story progresses, he could start to notice little things that Harry does which show his real intelligence. Ron's loyalty to Harry would then play a role in how he reacts to this discovery, either helping Harry keep it a secret or getting frustrated with Harry for not sharing his intelligence more freely.
A possible plot could involve a mystery within the village. Naruto, being smarter, is the first to piece together the clues and solve the mystery. Shikamaru, who usually excels in such situations, is left playing catch - up. Naruto could use his intelligence to not only solve the mystery but also prevent a greater disaster from befalling the village, showing that his intelligence is a valuable asset to the community.
Well, one interesting plot point could be how Harry uses his hidden intelligence to outwit his enemies. For example, he might come up with clever strategies during duels.
Maybe Harry discovers a new form of magic that Hermione has overlooked, and he uses it to solve a major problem in the wizarding world. This makes him seem smarter in that aspect.
Obviously, Harry is one of the main characters since it's about him being smarter than he seems.
In the 'harry shows his power fanfic', perhaps it's a story where Harry has to show his power in a wizarding competition. He might use his unique abilities like Parseltongue to outwit his opponents and prove his worth. He could also draw on his connection with the Patronus charm to protect himself and others during the tasks.
Well, without reading the actual fanfic, it could be about Harry Potter having hidden intellectual abilities that others around him, like his friends or teachers, don't fully recognize. Maybe he solves complex magical problems in ways that surprise everyone.
In the 'harry shows his slytherin side fanfic', it could be that Harry is influenced by Slytherin - related magic or a Slytherin - minded character. So he begins to value power and status more, and his actions become more devious. For example, he might manipulate situations to his advantage in a way that is more typical of Slytherin students. He may also form alliances with characters who have Slytherin - like qualities and distance himself from his Gryffindor friends.
Well, perhaps Harry uses his ice magic to create amazing sculptures in the Hogwarts courtyard. This would surely draw the attention of his friends and foes alike.
Maybe Harry is a thief to steal back something important that was taken from him or his family. For example, a magical heirloom that has been wrongfully confiscated.