Most likely, the main character is the boy ninja himself. There could also be his ninja master who teaches him the ways of the ninja.
The super ninja boy is the central figure. But there could be other characters like his best friend who is always by his side during his adventures. And perhaps an antagonist, an evil ninja or a powerful sorcerer who is trying to stop the super ninja boy from achieving his goals.
The main characters in the ninja turtle story are the four turtles - Leonardo, Donatello, Raphael, and Michelangelo, and their sensei Splinter, as well as the villain Shredder.
I'm not sure specifically, but there could be the Ninja Kid himself as the main character.
Since it's Ninja Kids Story, the main characters could be a bunch of young and brave kids. There might be a leader among them, who is very determined and smart. Another character could be the funny one, always making jokes even in dangerous situations. And there could be a shy but very talented kid when it comes to using ninja tools.
Often, the main characters are the ninjas themselves. They could be young trainees starting their journey.
I'm not sure exactly, but likely there are some cute ninja girls as main characters.
Ninja Hattori is definitely one of the main characters. And of course, his master Kenichi should be there too.
I don't know for sure, but it could be the ninja himself or herself as the main character. Maybe there are also some opponents like rival ninjas or samurais.
Goemon is the main character, of course.
The main characters are the three little ninja pigs and the big bad wolf. The three pigs are the protagonists, each with their own personalities and ninja skills. And the wolf is the antagonist who tries to cause trouble for the pigs.