Mimirin Midorihara is a white anthropomorphic snowshoe hare with pink-touched inner ears tipped in black, a forehead tuft, a pink nose, and a buck tooth. She always wears a pink ribbon near her left ear; her earring shifted from a red flower design after episode 99 of *Hesoka*. Her attire evolved: initially, she sported a yellow long-sleeved shirt under a red overall dress with light red shoes and white socks, switching to short sleeves seasonally. From *Hakken* episode 78, her outfit became a pink long-sleeved top featuring a yellow collar and gold button, paired with a cyan skirt, light red shoes, and pale pink socks, again using lighter fabrics in summer. In the *Wow!* series, she adopted a grey polka-dotted dress with a pink cardigan, pink Mary-Janes, and long blue socks, transitioning to a pink sleeveless dress with a beaded ribbon, grey shorts, and sometimes a tan sunhat in summer.

She lives on Challenge Island and attends Challenge Kindergarten. Her family runs Flower Shop Midorihara. Mimirin blends a gentle yet lively nature with occasional clumsiness and spoiled tendencies. Though often tearful, she shows determination facing challenges and bravery befriending kind souls. She possesses exceptional speed, outpacing her peers. Despite being a rabbit, she dislikes carrots and fears snakes, caterpillars, and insects. She loves dolls, flowers, and strawberry shortcake, her favorite food. Born October 10 (Libra), she has blood type B. She is an only child, a unique status among main characters since 2012.

Her friends include Shimajiro Shimano (befriended after overcoming his shyness), Torippii Sorano, Nyakkii Momoyama, and kindergarten peers Marurin Sasaki, Kikko Hayashida, and Sakurako Koinuma. Her childhood friend Ramurin Makiba, who gifted her the favorite ribbon before relocating to France, is significant. Her surname "Midorihara" combines "Midori" (green) and "hara" (fields); her given name "Mimirin" derives from "Mimi" (ears) and "rin" (dignified).

Mimirin participates in narrative quests like the Glittering Kingdom adventure, responding to crises alongside allies such as Shimajiro and Prince Pearl. She performs the solo character song "With a Wish...".