Yamabuki Saaya, a third-year student at Hanasakigawa Girls' High School, anchors the band Poppin'Party as its steadfast drummer. Her bond with Kasumi ignited during their entrance ceremony, sparking a daily ritual of shared lunches. Juggling academics with responsibilities at her family’s Yamabuki Bakery, she assists in operations while managing household duties and caring for younger siblings Jun and Sana.

Once a member of the middle school band CHiSPA, she withdrew after her father’s illness led her to miss a pivotal performance, fearing her absence would strain others. Years later, Kasumi’s unwavering resolve and her mother’s gentle nudges rekindled her musical spark, culminating in her joining Poppin'Party. A unique thread in her history involves exchanging diaries with Kasumi across separate classes, their bond sustained through handwritten notes at a shared desk.

Renowned for her serene composure and emotional intuition, she stabilizes the band during turmoil while extending a nurturing presence beyond it. She mentors peers like Tomoe, bonding over drumming and sibling care, and indulges Moca’s frequent bakery visits. Her reluctance to refuse favors surfaces in tutoring Hagumi, mirroring her selfless ethos.

Her passions span collecting hair ornaments, photography sparked by a design event, and immersing in romance films or Cinderella narratives. She employs an unconventional drumming style, wielding three sticks—a signature technique noted in media. Paradoxically, animals shy from her affectionate overtures despite her gentle nature.

She possesses royal blue eyes and chestnut curls swept into a high ponytail secured by a ribbon, with bangs framing her face. Her signature outfit pairs pale yellow trousers with a frilly white off-shoulder blouse. Culinary preferences lean toward garlic-chili spaghetti and cheese, while raw seafood disinterests her. Her name, blending "mountain" and "song/wind" (Yamabuki) with "sand" and "satin-silk" (Saaya), echoes familial heritage and lyrical symbolism.