As we don't have enough information about this 'the black plate story', the main characters could be a group of archaeologists who find the black plate during an excavation. They might then face various challenges and mysteries related to the plate as they try to understand its significance and origin.
Since I don't know the story, I can't say for sure. But it could be the person who owns the plate and has the associated trauma.
I'm not sure exactly who the main characters are without reading the novel. But they could be ordinary people who are thrown into extraordinary situations and have to step up. Maybe there's a young protagonist who is shy at first but then has to become more confident as the story progresses.
The 'the black plate story' could be about various things. It could be a fictional story where the black plate has magical powers. For example, it might be able to grant wishes when certain conditions are met. Or perhaps it's a story set in a historical context, where the black plate was used in some important ceremony or was a symbol of a particular group or culture.
The main characters could be the tectonic plates themselves. They are like the big movers and shakers in the story. For example, the Pacific Plate could be a character that is always on the move and causing all kinds of action like earthquakes and volcanoes.
There's David Mason too. He's involved in many of the key events in the main story, especially those related to the future part of the plot.
Since I don't know the exact details of this story, it's hard to say for sure. But if it's related to 'Black Clover', it could feature Asta, Yuno, and their friends. They are the main characters in the original 'Black Clover' series, so it's likely they would be involved in this black beach story as well.
Not having read 'the black farm story', it's hard to determine the main characters. However, they could potentially include a strong - willed black female farmer who is breaking gender and racial barriers in the farming world. Her children might also be main characters as they grow up on the farm and face different challenges. Additionally, there could be a local advocate who fights for the rights and success of the black farm in the face of external pressures like big corporations trying to buy the land.
I don't know for sure, but if it's about black eagles in nature, the main characters could be the eagles themselves. Maybe a male and a female eagle that are building a nest and raising their young.
Since I don't know the specific 'the black coffin story', it's hard to say. It could be the person in the coffin, or the people who discover the coffin.