Black Glasses in Grave Robber's Chronicles, also known as Black Blind, was an important character. He was a descendant of a Manchu noble, but his name was unknown. Black Glasses often wore a pair of sunglasses, and he always had a mysterious smile on his face. Even when he was surrounded by snakes, he had a relaxed smile. He was good at disguising and saber techniques, and was agile. Although his eyes could not see clearly in the day, they could see clearly in the dark. He had a deep relationship with Wu Xie, and Wu Xie was one of his disciples. As for the true identity of the black glasses and whether he was really blind, the current information did not give a definite answer.
Toge Inumaki is important too. His special cursed speech ability makes him stand out. Also, the principal of the school, Masamichi Yaga, is likely to be important as he is in a position of authority and has an influence on Gojo and the other students. There could be other characters like the members of different clans that also play roles in the complex web of the story.
One idea could be that the admiral with black hair and glasses is leading a space exploration mission to a distant and mysterious planet. The crew faces various challenges like strange gravitational fields and alien life forms, and the admiral's intelligence and leadership, symbolized by his glasses perhaps, help them through.
Another angle for the fanfic could be that the admiral is a bit of an outcast in the space military because of his distinct appearance with black hair and glasses. But his unorthodox thinking and unique perspective, which might be related to his appearance in some way, end up being the key to solving a major space - related crisis, like a malfunctioning star that threatens to destroy entire solar systems.