The main character, of course, is a very important one. His actions and decisions drive the story forward. Then there are his classmates. Some of them are rivals, like those who are also vying for the top positions in the school. And there are the teachers as well, who play a role in creating the rules and the overall environment of the school.
One of the main themes is competition. The story is set in a highly competitive school environment where students constantly strive to outdo each other. Another theme is intelligence and strategy. The main character has to use his wits to navigate the complex social and academic situations. Also, there is a theme of social hierarchy as the school has a strict class system.