I'm not sure specifically what the 'rocket sad story' is without more context. It could be about a rocket launch that failed, perhaps with the loss of a valuable payload or the end of an important space mission.
Meowth in Team Rocket has a sad story mainly because of his unrequited love for a female Meowth. He learned to speak human language in the hope of impressing her, but she still rejected him. This made him feel very sad and lonely, yet he continues his journey with Team Rocket.
Rocket Raccoon has a sad story. He was created through cruel experiments. He was taken from his home and turned into a weapon or tool by those unethical scientists. He was alone in a world that saw him as a freak. His only friends were those he found along his adventures like the Guardians of the Galaxy, but the memories of his past torment still haunt him.
" Black and White Double Demons " was a term with multiple meanings. The specific meaning depended on different cultures and context. In anime, legends, literature, and movies, there were their own black and white twin demons. In the anime series Detective Conan, the Black and White Double Demons referred to the characters Heiji and Kidd. In ancient Chinese legends, the Black and White Double Demons referred to the Black and White Impermanence. They were the messengers responsible for taking away the souls of the dead. In the literary work " Water Margins," the Black and White Double Demons referred to Zhang Shun and Li Kui. In addition, the Black and White Double Demons could also be used to describe two people or things with opposite personalities. In short, the specific meaning of the Black and White Double Demons varied according to the context.