Another possibility is that he's just had an argument with one of the other pups. For example, if he and Chase had a disagreement about how to handle a situation, and things got a bit heated. Marshall is a sensitive pup, and such an argument could really upset him and lead to him crying.
Perhaps Marshall has lost something precious to him. It could be his fire truck, which is not only a vehicle but also like a friend to him. Without it, he might feel powerless and sad. Also, he might be crying because he made a mistake during a rescue mission and is blaming himself for not being able to save someone or something in time.
Maybe in the fanfiction, Marshall made a big mistake that endangered the other Paw Patrol members. For example, he might have accidentally set off a chain of disasters during a rescue mission due to his over - enthusiasm and lack of caution.
Rubble would probably be really concerned. He's a good friend to Marshall and would try to cheer him up by offering him some of his favorite treats or by just sitting next to him and being there for him. Skye might fly around him, trying to make him laugh with her acrobatic stunts.
The Paw Patrol team would initially go through a period of disbelief. Rocky might isolate himself as he tries to come to terms with Marshall's death. Zuma would be quieter than usual, missing his friend. Ryder would have to step up and be strong for the team, but inside he'd be deeply hurt. They would also likely hold a memorial service for Marshall, with each pup sharing their favorite memories of him. This would help them start to heal and find the strength to continue their important work in Adventure Bay.
One possible reason could be that Ryder lost one of his pups in a dangerous mission. He might feel responsible and break down in tears because of his love for the pups.
It could be that she's homesick. Even though she has a great life with the Paw Patrol, she might miss her old home or her family. Or perhaps she saw something really sad in Adventure Bay, like an animal in pain that she couldn't immediately help. Skye has a big heart, and seeing such a sight could bring her to tears.
Yes, there are some hints of a special relationship between Marshall and Everest in Paw Patrol. They often work together and seem to have a great bond.
One possible fanfiction could be that Chase gets separated from the Paw Patrol team during a mission. He finds himself in a strange part of the forest. A little lost puppy comes up to him, crying because it's lost its family. Chase, being the brave pup he is, tries to comfort the little one. He uses his tracking skills to look for the puppy's family while also protecting it from any potential danger in the forest.
Marshall's character can also be developed through his relationships. For instance, having a bit of a friendly rivalry with another Paw Patrol member over who can handle the most difficult medical cases. This would bring out different aspects of his personality and how he copes with competition.
An old - fashioned fire engine that has come to life through some magical accident could be the antagonist. This fire engine believes that only it should be doing the firefighting in Adventure Bay and sees Female Marshall as a threat. It tries to block her path during emergencies and even tries to take over the Paw Patrol's fire station. Female Marshall would have to prove that she is just as good, if not better, at firefighting and show the living fire engine that teamwork is more important.
Another option is to simply do a general web search using keywords like 'Paw Patrol Chase Marshall fanfiction'. This may lead you to personal blogs or smaller fan - run websites that host fanfictions. However, be cautious of the sources and make sure they are reliable and appropriate.