Well, first of all, the genin teams would be regulars. They need to stock up on basic ninja equipment. Then, the older ninjas who are retired might visit to relive their younger days by buying things they used to use. And don't forget the wandering ninjas. If Naruto's shop becomes famous enough, they would stop by to buy rare items or get some rest and information at the same time.
His ninja friends like Sasuke, Sakura, and Kakashi would surely be regulars. Sasuke might come to buy things secretly to support Naruto's business. Sakura could be there to get supplies for her medical ninja work if it's a general store. And Kakashi would stop by for a chat and to pick up some new reading material if Naruto sold books.
Well, the regular customers could include some of Harry's old friends from Hogwarts, like Ron and Hermione. They would support Harry's business and enjoy the unique atmosphere. In addition to that, supernatural hunters from the Supernatural world might stop by. They could be looking for information about certain supernatural beings that might be lurking around the bar. And of course, there would be the local supernatural community, such as witches and warlocks who are not directly related to Hogwarts but are interested in the mix of magic and the new - found supernatural elements in the bar.
Other potion shop owners might visit too. Not as customers in the traditional sense, but more to check out the competition. They might be curious about Harry's unique potions. And then there are the local wizards and witches in the area where the shop is located. They could need potions for daily life, like a potion to make their gardens grow better or a potion to keep their pets healthy.
Some of the older villagers who have watched Naruto grow up would be regulars. They would come to support his business and also to reminisce about the old days. And don't forget the jonin who are always on the lookout for a good meal. They would appreciate Naruto's hard work and the unique atmosphere of his restaurant.
The regular customers could be Naruto's friends from the ninja academy. They would come to the bar to relax and catch up on old times. Also, other ninjas from the Hidden Leaf Village might stop by after a long mission.
Students from Hogwarts could be regulars. They might come during Hogsmeade visits. Also, young wizards and witches starting their careers in Diagon Alley would stop by. And of course, some of the older professors might pop in for a cup of their favorite brew.
His old friends from Hogwarts like Hermione and Ron could be regulars. They might come to support Harry's business and also to buy some useful things for their own magical lives. Maybe Neville would come to buy some special plants for his own gardening projects.
There could be students from a nearby school or college. They might come in for a quick snack or to study while having a coffee.
Fellow wizards or magic - users could be regulars. They might come to the bar to unwind after a long day of using magic. Some might be there to exchange stories about their magical adventures or to seek advice from Harry, who has his own share of extraordinary experiences. They could include a young wizard just starting out, looking for guidance from Harry, who is seen as a bit of a local legend in the bar.
I bet the regular customers would include some of Harry's old Hogwarts friends. Maybe Ron would stop by for a butterbeer and a chat. Hermione might come to relax after a long day of research. And of course, the Weasley twins would probably be there often, looking for new business ideas or just to have some fun.