He could meet a Japanese witch or wizard who becomes his best friend. This person could teach him all about Japanese magical traditions and how to navigate the Japanese wizarding world. For example, they might show him how to use a Japanese - style magic wand.
There could be a group of international wizards and witches in Japan who Harry befriends. They come from all over the world to study Japanese magic. Together, they form a sort of magical study group, sharing their different magical cultures and knowledge, with Harry contributing his own experiences from Hogwarts.
Perhaps Harry is on a sort of exchange program. He has to adapt to the Japanese wizarding school system. He makes new friends who introduce him to Japanese culture. They go on adventures together in Japan's beautiful and sometimes spooky landscapes, like exploring an old haunted shrine that has a magical secret within. Harry's presence also brings a new perspective to the Japanese wizards and witches about the outside magical world.
Perhaps he'll meet a mysterious old wizard who lives in a secluded temple in the mountains. This wizard could be a master of ancient Japanese magic and could teach Harry about the spiritual side of magic that is deeply ingrained in Japanese culture. Harry might also meet a group of young Japanese witches who are training to become magical healers. They could share their knowledge of Japanese magical plants and how to use them for healing, which would be very different from the healing methods Harry learned at Hogwarts.
Maybe Harry meets a group of magical creatures' protectors in Japan. They are dedicated to protecting the unique magical creatures in Japan, and Harry joins them in their adventures, learning a great deal about Japanese magical fauna along the way.
In a Sekirei fanfiction set in Japan, Harry Potter's story would take on a whole new direction. He would be exposed to Japanese mythology and magic which could be very different from what he learned at Hogwarts. The Sekirei themselves might have powers that are either complementary or in conflict with his own magic. His relationships with other characters would also be different. Instead of the typical Hogwarts friendships, he might form bonds with Japanese wizards or Sekirei based on different values and goals.
He could meet the Nords. They are a tough and hardy race, and Harry might learn a thing or two from them about survival in the harsh northern regions of Tamriel.
He might meet the samurai of Iron Country. These are warriors with different fighting styles compared to the ninjas. Naruto could learn a great deal from them, like their swordsmanship or their sense of honor.
In this kind of fanfiction scenario, it would be really interesting. Harry might have to adapt to Japanese culture while still having his magical abilities. Maybe he would attend a Japanese wizarding school that has some unique features inspired by Sekirei. For example, the school could have some sort of spirit - like the Sekirei - associated with it in a magical way.
He could meet new professors. These professors would have their own teaching styles and areas of expertise. They might introduce Harry to different aspects of American magic that he has never encountered before.
He could meet a famous wizard author who is signing books in Diagon Alley. This wizard could give Harry some valuable advice about his future.
Maybe he meets an exchange student from a different magical school. For example, a student from Beauxbatons or Durmstrang. They could share their different magical cultures and knowledge with Harry, and together they could face some challenges that require a combination of their unique skills.