Often, they are the ones who bring some sort of change or growth in the protagonist's life. They act as a catalyst, whether it's in the form of love, friendship, or mentorship. For instance, in some novels, the 'white moonlight' character helps the main character to overcome their fears or to pursue their dreams.
They often portray them as independent. For example, in 'The Hunger Games', Katniss Everdeen is a lone wolf in a sense. She has to rely on herself in the arena, making her own decisions to survive. She's not one to blindly follow the crowd. Another way is showing them as outsiders. Like in 'The Perks of Being a Wallflower', Charlie is an outsider, a lone wolf among his peers. He observes and experiences things on his own terms.
They are also shown as having a certain level of mystery. Take the character from 'Overlord' again. His true nature and the full extent of his powers are not immediately clear to other characters in the story, which adds to his allure as a 'boss' - like hero.
Typically, the widow is shown as strong yet vulnerable. In many widow romance novels, she has to deal with her own insecurities while also facing the judgment of society. The male character is usually there to support and love her unconditionally, which helps her to heal and open up to love once more.
In buccaneers novels, the characters are usually depicted as living on the edge. They are presented as having a sense of freedom that comes with the pirate life. They might be portrayed as lawless to some extent, but also with their own moral codes. Take Captain Hook in 'Peter Pan' for instance. He is a menacing buccaneer, yet he has his own set of rules within his crew. They are also shown as having a love for treasure and adventure, always seeking the next big score.
Stalker novels also sometimes show the bystanders or the people around the stalker and the victim. These characters can range from being completely oblivious to the situation to being enablers. In some novels, they add to the overall atmosphere of unease and mystery as they may or may not be aware of what's really going on.
In single mom romantic novels, the main characters, especially the single moms, are usually depicted as having a lot of love to give. They are loving towards their children first and foremost. When it comes to the romantic aspect, they are a bit hesitant at first because they are worried about how a new relationship will affect their children. The male characters in these novels are often understanding and patient, willing to accept the single mom and her child as a package deal.
They often portray the single parent as strong yet vulnerable. For example, in many novels, the single mother or father is shown to be doing their best to raise their children on their own, but at the same time, they are lonely and longing for a partner.
In 'honor bound novels', characters are often portrayed as having strong moral compasses. They stick to their principles no matter what. For example, a character might refuse to lie even if it would benefit them, because lying goes against their sense of honor.
Mercenary characters in light novels are often portrayed as tough and resourceful. For example, they might be skilled in combat, like being able to use various weapons effectively.
In swat romance novels, the SWAT characters are often portrayed as strong, brave, and heroic. They are shown as highly trained individuals who are good at their jobs. For example, the male lead in a typical 'swat romance novel' might be a fearless SWAT team leader. The female characters can be independent and feisty, like a journalist who is covering a story related to the SWAT team and then gets involved romantically.