One of the main characters could be a scientist. When the martian boy falls to earth, the scientist might be the first to discover him. The scientist would be curious about the boy's physiology and technology from Mars. Another character could be a young girl. She could befriend the martian boy and teach him about human emotions and relationships, which are very different from what he has on Mars.
Well, there could be a government agent as a main character. The agent's job is to keep the martian boy a secret from the public for security reasons. But as he spends time with the boy, he starts to question his orders. And then there could be a group of kids, like a gang of sorts. At first, they bully the martian boy but later they become his friends. They introduce him to the fun parts of Earth like playing games and going to parties, which helps the martian boy feel more at home.
Well, perhaps the young Martian boy is on a mission in his own planet but something goes wrong and his spaceship crashes on Earth. He then has to figure out how to survive in this strange new world with different gravity, air and cultures. He might meet some friendly humans who help him adapt and in the end, he could either find a way to go back to Mars or choose to stay on Earth.
Maybe his Martian friends.
Perhaps he'll discover an ancient Martian civilization. There could be old structures, artifacts, and knowledge that has been long forgotten on the surface. He could become the key to unlocking the secrets of this lost civilization, or he could accidentally set off some sort of mechanism that has been dormant for ages, which could lead to various consequences, either good or bad.
The main character is the astronaut who is left on Mars. I'm not sure if there are other really prominent characters without looking more closely at the story.
It might also be that the main characters are the spacecraft themselves. For instance, the Mars rovers like Curiosity or Perseverance. These rovers are like the protagonists in the exploration of Mars. They move around the Martian surface, take pictures, analyze samples and send back valuable information. They are designed and built by teams of engineers and scientists, but in a way, they are the ones directly experiencing the Martian environment and are central to the story of Martian exploration.
Often, the main character is still Mark Watney, the astronaut who was stranded on Mars in the original story. He continues to be the central figure as the fanfiction builds on his experiences.
A talking parrot might be a main character. The parrot has a sassy personality and knows all the gossip of the jungle animals. It helps the boy communicate with other animals in the jungle as it can speak multiple languages. It also adds a bit of humor to the story as it makes witty remarks about the boy's actions.
I'm not entirely sure without reading it specifically, but likely there's an explorer or a scientist as a main character.
There is usually a lead character, often an adventurous type, who is brave enough to take on the journey to Mars. There might also be some supporting characters, perhaps other members of the exploration team, who play roles in different parts of the story, like helping with scientific research or dealing with unexpected situations on Mars.
One main character could be a young scientist. This person could be intrigued by Loki's arrival and his other - worldly powers. They might try to study him in a non - invasive way, which could lead to some interesting interactions between them. Another character could be a street - smart kid who Loki befriends. The kid shows Loki the ropes of the city and in return, Loki protects the kid from the local bullies.