Well, in 'larry the scary story', Larry might be a character that is central to the horror elements. Maybe he is a victim, or perhaps he is the source of the scariness. For example, he could be a haunted figure or someone who has stumbled upon a dark secret, which then leads to all the terrifying events in the story.
Larry could be a relatable character in the story. He might be an ordinary person with ordinary dreams, but his need for a friend is what sets the story in motion. Maybe he has a kind heart and is just waiting for someone to notice him and become his friend. He could be of any age, but the common thread is his longing for friendship.
Since we don't have much information given, Larry in '600 lb life larry's story' is presumably an individual who has reached a weight of 600 lbs. He might be from anywhere, with different life circumstances that led to his extreme weight. He's on this show to document his journey of transformation. It could be that he has faced discrimination or has been unable to do things he loves because of his weight. His identity as Larry is tied to his story of facing the challenges of obesity and trying to overcome them with the help of the resources provided by the '600 lb life' program.
The city's diverse population has also had an impact. With different ethnic groups, cultures, and social classes coexisting, it gives writers a lot of material. In Chicago fictions, we can see stories about immigrants trying to make a living, or about the clashes and reconciliations between different groups. The city's rich history of labor movements, for example, has also inspired many fictional works that deal with the struggles of the working class.
I'm not certain who Larry Novak is without more context. He could be the author who created this original Christmas story, or perhaps a character within the story itself.
A crossover could involve a character from Chicago Fire having a personal connection to a case the Chicago PD is working on. Maybe a firefighter's family member is wrongly accused of a crime. The firefighter then teams up with the PD detectives to clear their family member's name. This would bring in elements of loyalty, family, and the different skills of both groups. They could share information and resources to solve the mystery.