Answer: Characters
Step-by-step explanation:
The correct answer is Characters. The riders can see their characteristics in the book because they are showing often in a story, that is why they are called like that.
Nice Guys and Protagonists are also parts of the Characters and Extras are those who are not showing often in a story so people cannot see their characteristics.
Nice Guys are ones from which the riders do not expect to do anything bad because of their behavior throughout the story and Protagonists are the main characters.