Tsugi is a gray patchwork plush cat crafted by Yuni to ease his loneliness. She features blushed cheeks, dark gray arms and legs, distinctive eyelashes, and a red star on her right ear. A red bow sits atop her head. Her right ear is dark gray, while Hagi's left ear is dark gray, marking a key physical difference between them.

Her speech consistently ends with the verbal tic "~tsugi". This, paired with Hagi's "~hagi", forms the Japanese word "tsugihagi" – meaning "splicing" or "patching" – reflecting her handmade nature.

Tsugi possesses unwavering loyalty to her creator, Yuni. She actively assists him in spreading Black Abysses to disrupt human dreams under the Queen of Nightmare's command. Later, she and Hagi begin working for a new antagonist, Akumu, while maintaining their partnership with Yuni.

Across all media, Tsugi's core relationships remain focused on Yuni, whom she deeply admires, and Hagi, her constant partner. Her character shows no significant independent development or expanded backstory beyond her initial creation and dedicated service to Yuni's objectives.