Kaasuke is a kappa, a water-dwelling yokai from Japanese folklore. He possesses turtle-like features: green skin, a shell, webbed hands, and a distinctive plate on his head surrounded by hair. In the narrative, he forges a partnership with Sora Yamamoto, an employee of the Japanese space agency JAXA. Kaasuke's driving motivation is his burning aspiration to travel to outer space. This dream fuels his collaboration with Yamamoto, who aims to train and prepare Kaasuke to become an astronaut capable of participating in terraforming efforts on Mars. Their ambitious joint objective focuses on adapting the Martian environment to support life, a mission that defies traditional kappa roles typically linked to rivers and lakes. The story positions Kaasuke as a figure who fuses yokai capabilities with human technological ambitions through this space-oriented endeavor.