I'm not sure as I haven't read the novel specifically, but usually main characters are those who drive the story forward, so it could be a protagonist who has a central conflict or goal in the story.
Since I don't know the exact 'blue lights novel', it's hard to say. But it could have a young protagonist who is curious about the blue lights. Maybe there's also an old sage - like character who has some knowledge about the blue lights and helps the main character on their journey.
There's no way to be certain without reading the novel. It might have a group of friends as main characters, and they all have different relationships with the blue lake. For example, one might be a local who has always known the lake's secrets, and another could be a newcomer who is intrigued by it.
There could be a female character who is very alluring and mysterious. She might play a crucial role in the story, like being the object of the protagonist's affection or the source of some kind of conflict. And there may also be an older figure, maybe a mentor or a villain, who influences the actions of the main character.
I'm not sure specifically as I haven't read the novel in detail. But generally, there might be a protagonist who is likely to be the one most affected by the 'patch of blue' element in the story.
In the 'the blue max novel', Bruno Stachel stands out as a main character. He is a pilot with great ambition. He is constantly vying for the Blue Max. Alongside him, there are other characters such as his superiors and fellow pilots. These characters together create a web of relationships that are full of rivalry, friendship, and the shared experience of the dangerous world of aerial combat in World War I.
As I haven't had the chance to read 'the blue and the black novel', I can't accurately name the main characters. However, if we assume that the colors are important, there could be a young protagonist who is initially attracted to the positive aspects of blue, like the beauty of the ocean or a clear sky. Then there might be an antagonist who is influenced by the darker side of black, like a shadowy figure from the protagonist's past who tries to bring chaos and despair. There could also be side characters who help the protagonist understand the balance between the blue and the black elements in their world.
The two main characters are often a young boy and a girl who are marooned together.
There could be an aristocratic family patriarch as a main character. He would be someone who upholds the family's traditions and values.
Yoichi Isagi is one of the main characters. He is a talented striker with a strong will to succeed. Rin Itoshi is also important, known for his great skills and competitive nature.
In 'the blue knight novel', apart from the blue knight, there could be a female character who is either his love interest or his rival. There might also be an old wise man who gives him advice on his quests.