Gaa-chan is a yellow duck-like figure inhabiting an animation studio. Beginning as an inanimate figure floating in a pond outside the studio, Gaa-chan comes to life and forms an inseparable bond with Baja, a small badger mouse residing there. Their deep friendship drives the narrative, centered on daily shared adventures exploring the studio. Gaa-chan is frequently depicted gently holding Baja's tail, a signature pose reinforced through merchandise.

Guided by the fairy Coco, Gaa-chan shares magical experiences with Baja. A key narrative sequence sees them using magic to fulfill their curiosity about the ocean after overhearing a studio director's wish to visit the sea, leading to a shared imaginative journey experiencing the ocean.

Gaa-chan originated from the unproduced project "Kanaka’s Magic Dream," conceptualized alongside Baja. Both evolved into Kyoto Animation's de facto mascots, appearing in official materials, instructional books, physical locations, and merchandise long before the OVA. Shouko Ikeda designed the character.

A sequel OVA, *Baja no Studio: Baja no Mita Umi* (Baja and the Sea), released in 2019. Gaa-chan's background, character development, and role remain confined to the interactions and established dynamic within the original special across all official media.