Hina Sakai is a tall, third-year high school student standing at 1.75 meters, making her the tallest among her peers. She possesses pale skin, long pink hair usually tied in a ponytail, and blue eyes, with a slender figure and notable bust size. Her school attire is the standard uniform or gym clothes like a white shirt and red bloomers, while casual outfits include a grey sleeveless shirt with a black skirt or a black top paired with blue micro shorts.

Her personality blends aloofness with hidden vulnerability. Initially perceived as mysterious, quiet, and socially reserved, she remains popular despite her reticence. This distance partly stems from her height, which historically placed her at the back of classrooms and limited interaction. Beneath this exterior, she harbors a strong fondness for cute objects, often personifying plush toys and talking to them alone. She exhibits tsundere traits, responding to flustering situations, especially when called "cute" – a rare compliment she distrusts initially – with cold stares or monotone speech. Her refined image contrasts with moments of physical clumsiness, like hitting her head on low ceilings.

Hina's background revolves around her family's local distillery, where she assists. She aspires to study marketing and production theory in Tokyo to modernize the business, leading to repeated clashes with her overprotective father who opposes her departure. This tension escalates until Hina runs away, seeking refuge at the Yorozuyo Inn. Her father challenges Kazuma Hoshino to a tug-of-war to resolve the dispute; Kazuma's victory enables Hina to pursue her education. Reconciling, she finds her father's sulking expression endearing and hugs him.

Her development unfolds through interactions with Kazuma and their friends. Early misunderstandings occur, like Kazuma admiring a charm on her phone, which Hina mistakenly believes is mockery. Her social anxiety prevents successful apologies. However, prolonged group activities gradually draw her out, making her more expressive. Her "cuteness proximity" reactions intensify, leading to comedic pursuits like chasing Ui Nakatsugawa in a penguin costume during a school race or giving affectionate head-pats to Ayumu Hoshino. She also displays poor alcohol tolerance, becoming intoxicated easily. A significant moment happens when Kazuma accidentally encounters her partially undressed in his room, resulting in her forgetting her bra.