Miki Murakoshi is Mayu Morita's closest friend and primary social counterpart. Exceptionally talkative, energetic, and outgoing, she naturally dominates conversations. This contrasts sharply with Mayu's silent nature, resulting in frequent one-sided dialogues where Miki effortlessly deciphers Mayu's minimal responses thanks to their long-standing familiarity.

She actively pursues romantic interests, developing crushes on multiple boys, yet her attempts never quite materialize into relationships for various reasons, leaving her perpetually single despite persistent efforts. Another recurring passion is her enthusiastic following of a daily soap opera starring actress Ako Waki.

As childhood friends, Miki shares a deep, understanding bond with Mayu that transcends verbal communication. She recognizes Mayu's silence stems from overthinking rather than disinterest or shyness. Miki actively encourages Mayu to overcome communication challenges by advising her to approach life with a smile. Their foundational friendship endures, with Miki steadfastly considering Mayu her best friend despite their contrasting personalities.

Within their friend group, which includes Chihiro Miura and Hana Matsuzaka, Miki's talkative nature fuels comedic situations through misunderstandings. Her jokes sometimes unintentionally trigger awkward moments, particularly when references to topics like broken families distress Hana, who experiences domestic strife. Male classmates Kōichi Ōno and Ryūta Kokubo frequently misinterpret Miki's interactions with Mayu and others as yuri scenarios, adding another humorous layer to her social engagements.

Miki Murakoshi's role remains consistent across the anime's two seasons, OVAs, and related media, defined by her genki girl traits, motor-mouth tendencies, and unwavering supportive friendship with Mayu, without substantial character development or background expansion.