Well, in a sad cat story, it could be due to abandonment. Maybe the cat was left behind when its owners moved. It could also be because of illness. If the cat was sick and there was no one to take care of it properly, that would be really sad. Also, competition for attention, like when a new pet comes into the household and the cat is no longer the center of attention.
One possible reason could be the loss of a loved one, like in the case where the cat's owner died. Another might be separation from friends or family, as the cat that lost its mouse friend. Or neglect, such as when the family focused on the new baby instead of the cat.
Financial difficulties might also play a part. If they were in debt or lost all their savings due to some unforeseen circumstances, it could have caused a great deal of stress and sadness. Their relationships might have suffered as a result, and this could be the sad story of Jamich.
One reason could be neglect. If the owner doesn't take proper care, like not feeding it enough or not providing shelter, the horse would be sad.
One reason could be the difference in their destinies. Silver is often tied to the future of his own world, while Blaze has her own duties in her dimension. This can lead to a sense of separation and sadness. For example, if Silver has to go back to his time to fix things and Blaze can't leave her world, it's a sad situation.
One possible reason is the pressure of always having to be perfect. As a virtual idol, Miku is expected to look and perform flawlessly all the time. Any glitch or mistake could be seen as a failure, which might make her sad.
Another reason could be unrequited love. As I mentioned before, if Meowth has feelings for another but is rejected, that's very painful. It can lead to a long - lasting sadness.
In some stories, the forest or a special place with strong natural magic can be the cause. The girl might unknowingly step into a place where the magic is so concentrated that it changes her form. This could be a place that has been untouched for centuries and has its own will to transform those who enter it into something more in tune with nature, like a cat.
One reason could be neglect. If the owner doesn't take proper care of the black cat, like not giving it enough food or a warm place to sleep. For example, leaving it outside in the cold winter without shelter.
One possible reason could be jealousy. If either A or J was a jealous person, it might have caused problems in their relationship.
One reason could be bullying at school. Other kids might pick on him because he's different in some way, like being too shy or having an unusual hobby. This can make him feel really sad and isolated.
It could be that Alan was betrayed by someone he trusted deeply. A friend or a business partner might have let him down, and this betrayal would make him feel sad and lonely, as it shatters the trust he had in people.