Fushi is a supporting character from the 2026 anime film Cosmic Princess Kaguya!. Fushi is a small, fluffy creature whose appearance is often compared to a sea slug. This being serves as the constant companion and partner to Yachiyo Runami, the popular AI virtual idol who administrates the Tsukuyomi cyberspace.

Fushi's origins are directly tied to Kaguya, the film's titular character from the Moon. Before becoming Yachiyo's partner, Fushi was originally known as InuDOGE, a virtual pet belonging to Kaguya during her time as a streamer in the Tsukuyomi world. After Kaguya was forced to return to the Moon, she attempted to travel back to Earth but her spaceship collided with an asteroid, sending her eight thousand years into the past. Trapped within her damaged vessel, Kaguya could not directly interact with the world. In this situation, Fushi served as her communicator and connection to the outside world, acting as an intermediary between the stranded Kaguya and humanity across the centuries.

As ages passed and human technology eventually developed the internet and the virtual space of Tsukuyomi, Fushi's role became crucial. It was through this companion that Kaguya, now existing as the digital avatar Yachiyo, was able to connect to the virtual world and ultimately reunite with Iroha Sakayori, the human who had originally found and raised her. Fushi thus acts as a vital bridge across time, enabling Yachiyo's presence in Tsukuyomi and facilitating the film's resolution.