Dead Sun - Side Characters

Concept arts about some of the side characters in Dead Sun: At first, Dr. Cereza didn't have too much role in the story other than being a narrator and the doctor at the beginning, who explains the situation to Zachary. But then I realized she could have further roles and development, as she continues to work as a doctor and provides the main character with medicines, and getting into conflict with the advenas.
Flinter is a secondary - vice commander beside Zachary, who also gives orders to the main military unit, while they protecting the Midnight-region against the aliens. He doesn't have too much role in the story, but he symbolizes some sort of hope and someone to look up to in this cold and dark world.
Sebastian 7K is a rather enigmatic character, appearing later in the story. He served in the same unit as Zachary back on Earth, but now he is imprisoned by the advenas.