Coo Erhard is a member of the Black Gema Gema Gang, a troupe led by Piyoko that frequently clashes with Dejiko and her friends. First appearing in the *Di Gi Charat Christmas Special*, he sports a dog tail, a canine-themed cap, unkempt dirty blonde hair, and reddish-brown eyes. Though his boyish looks suggest immaturity, he demonstrates sharp medical skills, acting as the group’s capable doctor. His demeanor balances a brash, self-centered streak—often rebelling against authority—with an otherwise easygoing attitude. While prone to brief squabbles, he typically remains unflappable, navigating conflicts with casual indifference. The Black Gema Gema Gang itself transitions from chaotic schemes in earlier stories to humorous or cooperative roles, such as partnering with Dejiko’s crew for seasonal festivities. Episodic specials like the *Ohanami Special* showcase Coo joining rivals for tranquil cherry-blossom picnics or shared performances, illustrating fleeting truces. These collaborations, including theatrical or musical ventures, remain circumstantial, never compromising his loyalty to the gang. His documented appearances focus on episodic scenarios rather than in-depth backstory or lasting growth.