Isamu Wakabayashi is the younger brother of Iori Wakabayashi, the female lead of the series. He is depicted as a young man with blond hair cut to ear length and brown eyes, and he has the appearance of a teenager. His role in the story is primarily as a supporting character who provides comedic contrast to the main romantic antics of his sister and her coworker, Habahiro Hige.

Personality-wise, Isamu possesses a notably inflated self-image. He views himself as a handsome and successful womanizer, a perception that is sharply contradicted by reality. Despite his confident claims of romantic prowess, he is in fact a virgin, a disparity between his self-perception and his actual experience that is a primary source of his character's humor. This disconnect contributes to odd and amusing behavior, and episodes featuring him are often considered among the most entertaining in the series.

His motivations are not deeply explored, but his actions are heavily centered on his relationship with his sister, Iori. He demonstrates a clear sister complex, showing an unusual and often comical preoccupation with her romantic life. This dynamic adds a layer of familial interference and awkwardness to Iori's already complicated pursuit of Hige. He is part of the small supporting cast that helps to develop the show's world and create situations outside of the main office setting.

Isamu does not drive the main romantic plot, which belongs to his sister, but serves as an obstacle or a chaotic element within it. His presence often shifts the focus from Iori and Hige’s awkward, marshmallow-centric interactions to a different kind of eccentricity. He has no notable abilities related to the workplace or romance; his function is essentially to be a living contradiction of his own delusions, which creates friction and humor in his interactions with his sister and other characters.