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.
A great character interaction could be between Severide from Chicago Fire and Voight from Chicago PD. Severide's laid - back but confident attitude could clash or complement Voight's tough and no - nonsense approach. They might start off not seeing eye - eye but then come to respect each other as they work towards a common goal, like solving a crime that is related to a fire incident.
One idea could be a joint emergency situation where a building fire is also a crime scene. Maybe the arsonist is still on the premises and the teams from both Chicago PD and Chicago Fire have to work together. The PD has to search for the suspect among the chaos and the firemen have to put out the fire while also trying not to destroy evidence.
You can try fanfiction websites like Archive of Our Own (AO3). It has a large collection of fan - created works, including many Chicago Fire crossover fanfictions. Just use the search function and type in 'Chicago Fire crossover' to find relevant stories.
One great Chicago Fire crossover fanfiction could be the one where they cross over with another popular show like Chicago PD. In such stories, the characters from Chicago Fire might collaborate with the police in some high - stakes situations. For example, a fire might be part of a crime scene and they have to work together to solve the mystery and also deal with the fire situation.
Voight from Chicago PD would be really interesting. He has a strong personality and his no - nonsense attitude would contrast well with the more team - oriented and often more laid - back firefighters. His detective skills could also be crucial in solving a crime that intersects with a fire - related situation.
A fanfiction might focus on Peter Mills' relationships at the firehouse. For example, his friendships with the other firefighters. He could get into an argument with one of them over a difference in approach to a job, but then they work it out and their bond becomes even stronger.
Protection. Given that it's a show about firefighters, protecting the baby from harm, whether it's from a fire or other dangers in the city, is a big part of the fanfiction. The characters will go to great lengths to keep the baby safe.
In a fanfiction like this, the father of Sylvie's baby could be a mystery at first. It could create a lot of drama and speculation among the characters in the firehouse. Maybe she goes through different emotions like fear, excitement, and worry all at once. She might also worry about how the baby will fit into her life which is already full of high - stress situations and long hours at work.