One possible theme could be loneliness. Fat Mike might have felt alone in certain situations, which made his stories sad.
Betrayal could also be a theme. If someone close to Fat Mike, like a friend or a family member, betrayed his trust, it would be a very sad story.
If 'Fat Mike' is a particular person in a certain community or group, perhaps the sad stories could be about his experiences like facing hardships in relationships, or difficulties in achieving his dreams. Maybe he had some losses in his career or had to deal with the loss of loved ones. But again, this is all speculation without further details.
One possible theme could be abundance. Since it has 'fat time' in the title, it might be about times of plenty, whether it's in terms of resources, relationships or experiences.
Another theme could be about the cruelty of fate. Take the case of a hard - working farmer who finally had a good harvest coming but then a sudden storm destroyed everything. All his efforts were in vain, and he was left with nothing but despair.
Self - discovery could also be a theme. Perhaps Mike King went through a period of his life where he was trying to figure out who he was, what his purpose was. This could involve traveling, trying different jobs or hobbies until he found his true self and that could be a significant part of his story.
One possible theme could be survival if the encounter with the coyote was in a dangerous or challenging situation. Mike Plant might have had to use his wits to survive.
One sad fat kid story could be about a kid who gets constantly bullied at school because of his weight. Other kids make fun of him during gym class or in the cafeteria. He feels so alone and sad, but doesn't know how to change the situation.
One possible theme could be patriotism. Since 'Stars and Stripes Forever' is a patriotic song, Mike's story might revolve around his love for his country.
A third possible theme could be the struggle between good and evil. Given that the 'Man of Steel' world often features battles between Superman (representing good) and various villains (representing evil), Mike could find himself caught in the middle of this struggle. He may have to decide which side he wants to be on or find a way to promote good in a world full of danger and evil.
The theme of change is also likely. A family being apart is a significant change in Mike's life. His relationships with family members will change, his living situation may change, and his own identity within the family might also change. The story could explore how Mike navigates through all these changes and what he learns from this experience of a family being apart.
One possible theme could be friendship. Despite their differences in appearance and origin, they could form an unlikely friendship in the fanfic.