The protagonist is surely an important character. They are often the center of the story, through whose eyes we experience the events in the novel.
There might be a mentor - like figure. In many novels, there is someone who guides the protagonist, gives them advice or helps them grow. In 'A Piece of the World Novel', this could be an older character with more life experience. For instance, it could be an old neighbor who has seen the changes in the area over the years and imparts wisdom to the main character.
In the Loguetown arc novel, the most prominent character is Luffy. He drives the story forward with his actions and dreams. Then there's Smoker, the Marine who is constantly trying to stop Luffy. Buggy the Clown is another important one. His presence creates some comical and dangerous situations. The Straw Hat crew members are all important too. Zoro's strength, Nami's navigation skills, Usopp's inventions, and Sanji's cooking are all integral to their time in Loguetown. For example, Sanji might be looking for special ingredients while in town.
Ace himself is the most important character, obviously. His personality, his powers, and his journey are central to the novels. Luffy also plays an important role as his brother. Sabo is another significant character, as they were all like brothers when they were young. And there are the various pirates and Marines that Ace interacted with during his adventures.
Mat Cauthon is an important figure. He is Rand's friend, with a roguish charm and a mysterious connection to a dagger that brings him both trouble and power. Egwene al'Vere is also crucial. She is a strong - willed woman who begins to learn magic and has her own journey of growth and discovery in the story.
I'm not sure specifically as I haven't read this exact 'home and the world novel'. But usually, there would be a protagonist who serves as the main lens through which we view the relationship between home and the world. This character might be someone who is caught between the two, trying to navigate their place in both.
There's also Strangman. He is an interesting character who has a different approach to the drowned world compared to Kerans. Strangman seems more interested in exploiting the situation for his own gain in some ways, which creates conflict within the story. Another character is Beatrice Dahl, who has her own role in the complex web of relationships and the overall story of survival in this new world.
The protagonist, Haruyuki Arita, is very important. He is an overweight boy in the real world but becomes a powerful figure in the accel world. Then there is Kuroyukihime. She is a skilled and mysterious girl who plays a crucial role in Haruyuki's journey in the accel world.
In this novel, perhaps there is a rebellious character who challenges the existing order and is at the forefront of the awakening. There might also be a family member of the main character, like a parent or sibling, whose relationship with the main character is affected by the awakening process. And then there could be a mysterious character who appears at crucial moments and has some kind of special knowledge related to the awakening.
Calantha is also significant. She is Henry's wife and her character helps to show the role of women in this world, both in terms of their relationships with men and their own agency within the constraints of the society.
Sanji is a key character. His cooking skills keep the crew fed and his chivalrous nature adds a lot to the story. Another important one is Robin. Her knowledge of the ancient Poneglyphs is vital in uncovering the secrets of the world in One Piece. Usopp also has his significance. His lies and his growth as a brave fighter are interesting parts of the story.
There's Roberta Muldoon. She is a transgender character, which was quite revolutionary for the time the book was written. Her friendship with Garp adds depth to the story. Also, Helen Holm, Garp's wife, is an important character as she plays a significant role in Garp's personal and family life.