Haruo Kasuga, a 21-year-old member of the Eden of the East group, displays a consistently anxious personality marked by nervous tendencies. During group meetings, he frequently seeks refuge under rolltop desks as a behavioral response to his unease.

He contributes computer skills to the collective efforts of Eden, aligning with the technical expertise common among members, though his role involves no significant leadership or specialized tasks.

Kasuga shares a close friendship with fellow Eden member Satoshi Osugi. His attentiveness to others emerges when he becomes the first to notice Osugi's unexplained disappearance after a shared dinner, despite his typically reserved demeanor.

The character also demonstrates perceptiveness regarding others' true motivations.