Mashiro Kurata attends Tsukinomori Girls' Academy as a second-year student, initially crushed by the pressure of talented peers after realizing her dream of entering the prestigious school. Daily sorrow defined her life until witnessing Poppin'Party perform at CiRCLE, an encounter that ignited transformative inspiration. Quietly reserved and shy, she often spirals into negative thinking, fearing she makes poor first impressions or seems odd to others. Yet she harbors a vivid imagination, losing herself in elaborate daydreams of flying whales or sky-soaring adventures—especially when crafting lyrics. She avoids horror genres and spicy foods as a picky eater but adores fantasy media like the "Fairy Legends" series and its marshmallow rabbit character.

Poppin'Party discovered her reviewing a band recruitment flyer at CiRCLE, where she lamented that bands weren’t as fun as she imagined and declared she wouldn’t return, leaving them bewildered. She later co-founded Morfonica, becoming its vocalist and primary lyricist. The band’s name embodies "metamorphosis," mirroring her yearning for growth. Her journey revolves around recurring self-doubt: early band struggles centered on feelings of inadequacy, while the "Blossoming Symphony" event saw similar challenges require bandmate support to endure.

In the OVA "Morfonication," a casual remark from former classmates—implying she hadn’t changed—plunged her into severe emotional turmoil, complete with hallucinations. Though Morfonica reassured her of her progress, the resolution underscored her insecurities as an ongoing battle. External friendships aid her growth too, particularly with Rokka Asahi. Bonding during "Little Rose Harmony," they playfully debate who admires Poppin'Party more, steadily nurturing mutual confidence. Physically, Mashiro has light blue eyes and shoulder-length bluish-white hair, standing 154 cm tall. Her original casual outfit paired a striped cyan dress over a white shirt with an indigo bow, ankle socks, and brown Mary Jane shoes.