The main character is of course the Ninja Kid himself. He is often brave and resourceful.
I'm not sure specifically, but there could be the Ninja Kid himself as the main character.
Perhaps there are some friends of the Flamingo Kid that are main characters as well. They could be different in personalities. For example, one could be really brave and the other very clever, and together they make the stories more interesting by complementing the Flamingo Kid's own traits.
In 'Snow White', Snow White is the main character. The seven dwarfs also play important roles. In 'Hansel and Gretel', Hansel and Gretel are the main characters. In 'The Velveteen Rabbit', the velveteen rabbit is the main character, and the boy who owns the rabbit also has a significant part in the story.
It's hard to say exactly who the main characters are without reading the 'casa kid stories' specifically. But they could be kids like you and me, or perhaps some friendly animals.
Often, the main character is the Samurai Kid himself. He's usually a young boy with a strong will to learn the ways of the samurai.
There are many interesting Ninja Kid Stories. For example, the ones where the ninja kid uses his martial arts skills to save his friends from bullies. It shows his courage and the importance of standing up for others.
The main character is the woman at the well. She is a Samaritan woman who has had a difficult life and has made some mistakes in the past.
The main character is Ferdinand, of course. He's the gentle bull. There are also the other bulls in the bullpen who are more interested in fighting. And there are the small animals like the birds and the mice that interact with Ferdinand.
The main character is Greg Heffley. He's the one through whose eyes we experience all the spooky events. His family, especially his older brother Rodrick who likes to play pranks that sometimes turn into really spooky situations for Greg, are also key characters. Additionally, his friend Rowley, who often gets dragged into Greg's adventures, whether spooky or not, is another important character in 'Wimpy Kid Spooky Stories'.
I'm not sure who the main characters are exactly, but I assume there is at least the 'fat kid' as a central figure. There might also be family members like parents or siblings who play important roles in his story.