From what is seen from the series, C-class is the first class to consist of extremely human-like demons, not resulting from a loss of power or transformation, whose only unusual features are different colored hair (or skin) and the occasional non-human feature such as pointed ears or horns. Personality-wise, there is wide variety, there are some that are arrogant and sadistic, but smart enough to not overestimate their strength; or eccentric ones like Chu and Jin who are carefree and optimistic. In short, C-class is the equivalent of normal humans, each with their own personality and views on life, but still have an interest in battle and retain instincts to guide them, while they rely more complex strategy to defeat enemies, rather than the threats of E-class and physical power of D-class