Sakura might be one of the characters. She has her own set of skills in the medical and combat fields. Meeting Harry could lead to exchanges of knowledge about different forms of healing and combat magic.
There's also Kakashi. With his Sharingan and vast combat experience, his interaction with Harry could be full of surprises. They could learn from each other's strategic thinking when it comes to facing opponents.
Well, it could be about Harry using his magic skills in the Elemental Nations. Maybe he'll learn new forms of magic there or make new friends with people who have elemental powers.
He could meet the main characters from Death City. For example, Maka Albarn and Soul Eater Evans. They could be initially cautious around Harry but then become friends as they realize his good intentions.
He could meet an Egyptian wizard who is an expert in ancient magic. This wizard could teach Harry a great deal about the history of magic in Egypt.
There might be an old sage living in the mountains of one of the elemental nations. The sage has vast knowledge of ancient ninja arts and has been in isolation for years. Naruto's encounter with this sage could be a turning point in his journey, as the sage could offer him wisdom and perhaps even a new form of power or training method.
Obviously, Buffy would be a major character he'd interact with. They could start off as wary of each other but then grow to respect one another's fighting skills. Giles too, as he has a wealth of knowledge about the supernatural, and he and Harry could have some interesting discussions about different types of magic.
He could meet Bella. Since Forks is Bella's hometown in the 'Twilight' series. They might become friends or have some kind of adventure together.
He could meet a young and talented French wizard who becomes his guide in France. This wizard might show Harry all the hidden magical spots in France.
He could meet a Canadian wizard named Oliver who is an expert in ice magic. Oliver could teach Harry how to use magic in the cold Canadian climate.
He could meet the ghosts of his ancestors. These ghosts might offer him some advice or reveal some family secrets that could help him in his future adventures.
He could meet other young wizards and witches who are also on vacation. They might be from different parts of the wizarding world. For instance, a group of wizards from a far - off land with unique magical traditions.