Without knowing the actual 'time to say please story', it could be various characters. It could be a teacher and students in a school environment. The teacher might be using the story to teach the students about polite communication. The students could be the main characters who either learn quickly to say 'please' or are reluctant at first but then understand its significance through different events in the story.
In the case of saying goodbye to a pet, the main characters would be the family members or the owner of the pet. They are the ones who are directly involved in the emotional journey of saying goodbye.
I don't know since I haven't read it. There could be a hero who is caught up in a series of events that prevent him from saying goodbye. Maybe a young man or woman.
Since we only have the title, it's hard to say for sure. But as the title mentions 'Uncle', he's likely to be one of the main characters. There could also be other family members like nieces, nephews, or siblings who interact with Uncle during the Christmas story.
It might be a story centered around a parent and a child. The child could have left home in a hurry, perhaps to pursue an opportunity far away, and the parent was left with no chance to say goodbye. So the main characters would be the parent, filled with worry and the child, full of eagerness for the new adventure but unaware of the pain of the unsaid goodbye.
Finn, a brave and curious human, and Jake, his magical dog buddy, are central to Adventure Time main story. Princess Bubblegum is another important character. She's intelligent and has to deal with the governance of the Candy Kingdom. The Ice King, with his ice powers and his obsession with kidnapping princesses, is also a key figure. There's also Marceline the Vampire Queen, who has her own unique personality and backstory that ties into the main story in various ways.
I'm not sure as I haven't read the specific 'never say goodbye novel'. But usually, in a novel with such a title, there could be a protagonist who is very determined and has a strong will. This character might be someone who has experienced loss but refuses to let it be the end, so they keep on trying to hold on to what they cherish.
I don't have enough information to determine the main characters in 'say goodbye visual novel'. It could be a young couple if the story is about a romantic relationship ending. Or it could be a group of friends if it's about parting ways after a long time together.
Since I haven't read the 'the story of time novel', it's hard to say who the main characters are. However, they might be characters who are on a quest related to time. For example, they could be searching for a way to reverse time, or to understand the true nature of time, and their journey forms the core of the story.
As I haven't read the 'no time for fear story', it's impossible for me to determine the main characters. It could be ordinary people put in extraordinary circumstances, or it could be some kind of heroic figures. But without reading it, it's just speculation.
The main characters are the parents and their two children. The parents are the ones who are initially in control of the house with all its technology. The children are the ones who get too attached to the virtual veldt in the nursery.