Hidarin is a supporting character who appears in the third season of the series. She is a member of the underground idol pop group OTMGirls, where she serves as the drummer and one of the backing vocalists. In terms of background, her name is derived from the Japanese word for "left" (hidari), which reflects her consistent positioning on the left side when the group is featured together. She is also identified as the twin sister of her bandmate, Migi, whose name means "right".

Physically, Hidarin is an anthropomorphic character with gray and white fur. She has large black pupils, each adorned with a single curled eyelash on the outer top side, and rosy pink cheeks. Her hairstyle features three strands tied back with a white and pink plaid bow, and she wears a white schoolgirl outfit complemented by a matching plaid bow at the center, a coordinating skirt, long white socks, and shoes.

Hidarin possesses a highly excitable and cheerful personality, though she is not portrayed as being particularly intellectual. Despite this, she has a keen sense of observation and can read people's emotions and intentions accurately. She is almost always seen in the company of her twin sister, Migi, and at times can become completely absorbed in her own private world. Her primary motivation is tied to her role within OTMGirls, contributing to the group's performances and activities. The band and its manager, Hyoudou, become a significant part of the main character's life, as Retsuko begins working as their accountant to pay off a debt.

Hidarin's role in the story is primarily as a member of this idol group, which serves as a central plot device in the third season. Her key relationships are with her fellow band members. Most prominently, she shares an inseparable bond with her twin sister, Migi, as they are nearly always seen together and function as a pair. She also interacts closely with the third member of the group, Manaka, and their manager, Hyoudou. Regarding her development, while her core personality remains consistent, she participates in the group's growth as they transition from an underground pop act to a band performing at a rock festival, requiring them to learn musical instruments. In a later plot development, both Migi and Hidarin participate in a scheme to assist Retsuko and her coworker Ton, disguising themselves as an auditing firm to help expose corporate fraud, demonstrating their willingness to aid others beyond their idol activities. Her notable abilities include her skill as a drummer and backing vocalist for the OTMGirls, as well as her previously mentioned talent for being observant and perceptive about the people around her.