There's an astronomer in 'Nightfall' who plays a crucial role. He's the one who discovers and tries to warn others about the coming nightfall. Another important character could be the religious leaders. They have a certain view of the world based on the constant light, and their reactions to the idea of nightfall are significant in the story.
Well, one popular type of character is the scientist - adventurer. These characters use their scientific knowledge to solve problems and uncover secrets. For example, Dr. Sarah in Isaac's works is constantly making new discoveries. There are also the rebel characters who fight against oppressive systems. They are often the ones who inspire change in the fictional universes. Another type is the artificial intelligence characters. Some are friendly helpers, while others turn out to be the antagonists due to glitches or malicious programming.
I'm not entirely sure as I haven't read the story lately. But typically in Asimov's works, the main characters are often intelligent, inquisitive individuals. In 'Youth', they might be young people with a thirst for knowledge or adventure.
In the Isaac story, there are several key characters. Isaac is at the center. His father Abraham is a major figure as he was the one who received the command to sacrifice Isaac. Sarah, Isaac's mother, is also important as she was part of the story of Isaac's birth. And Rebekah, Isaac's wife, is a main character too because she was brought into Isaac's life to continue his family line.
One common theme is the power of partnership. Since both Tarnished and Malenia are strong in their own ways, their coming together to achieve a common goal is often explored. For example, they might fight against a powerful enemy that neither could defeat alone.
Ranni often plays a guiding role in fanfiction plots. She has knowledge about the world and its secrets that the Tarnished needs. The Tarnished, in turn, is the one who can take action. For instance, Ranni might point the Tarnished towards a powerful artifact, and the Tarnished will go on the perilous journey to obtain it.
One memorable character is R. Daneel Olivaw from the Robot series. He is a robot with a highly developed sense of ethics and morality, often finding himself in situations where the Three Laws of Robotics are put to the test. His interactions with human characters, like Elijah Baley, are really interesting.
The main characters in this story are Isaac and his mother. Isaac is a young boy, innocent and vulnerable. His mother, on the other hand, is a complex character. She is deeply religious, but her religiousness takes a very extreme form. When she hears the so - called voice from God asking for Isaac's sacrifice, she is ready to go through with it. Their relationship and their actions form the core of the 'The Binding of Isaac Original Story'.
I'm not sure as there are many of his works that could potentially be considered a'school story'. But it could be students, teachers, or school administrators. Maybe a brilliant student who is the protagonist and faces various challenges in the school.