Eru Kusaba, a 17-year-old high school second-year student, performs as part of the comedy duo JK Cool alongside Arashi Waraino under Yoshimoto Kogyo. She stands 1.57 meters tall, weighs 50 kilograms, and has measurements of 81-56-80. Her appearance features long blonde hair typically secured in a ponytail and emerald green eyes. Eru's standard outfit consists of a navy button-up jacket worn over a white dress shirt with a red bow, a black skirt, and brown penny loafers, often accessorized with a taffy pink scrunchie around her left arm.

Personality-wise, Eru displays an exuberant and light-hearted nature, openly embracing her preference for moving at her own pace—a trait contrasting with her partner's more restrained persona. Within JK Cool, she fulfills the "idiot" (boke) role in their routines, delivering humorous or nonsensical lines that prompt reactions or corrections from Arashi, who serves as the "straight man" (tsukkomi). Both Eru and Arashi hold recognition as winners of a comedy tournament prior to their activities in the series.