Eigo Kohitsuji is a supporting character residing in the Black Doggy House dormitory at Dahlia Academy. He possesses tan skin and dark violet hair styled with bangs that obscure his eyes, along with sharp teeth. He wears the standard Black Dogs high school uniform.

His personality is marked by overt perversion, widely known among peers. He actively shares pornographic magazines and frequently behaves according to this trait. Despite this, Eigo displays loyalty to friends and consistently joins group activities with fellow delinquents Chizuru Maru and Kento Tosa. While initially hostile toward the rival White Cats faction—even participating in an attempted assault on Juliet Persia—his stance lacks deep ideological hatred. He acknowledges the attractiveness of both Juliet and Chartreux Westia and finds amusement in their interactions with Romio Inuzuka. After Leon Inugami advocates segregation in a bloodthirsty speech, Eigo comments that such extremism would leave them no one to bully, revealing his indifference to the White Cats' presence.

Within the narrative, Eigo primarily engages in comedic or antagonistic group actions. He provides Romio with pornographic material, leading to an awkward discovery by Juliet. During a beach episode, he nearly kisses Romio to demonstrate romantic tactics, causing mutual disgust. His delinquent activities include joining an attempt to kidnap Juliet, thwarted by Romio. Over time, he shows subtle shifts like passively accepting Romio and Juliet's relationship, though he remains a secondary figure without major individual development.

His name, Eigo Kohitsuji, translates to "Old Sheep English," referencing the Old English Sheepdog breed—a connection reinforced by his hair covering his eyes like the dog's fur. His surname combines the characters for "old" (古) and "sheep" (羊), while his given name means "English language" (英語).