Yae Niizuma is an 11-year-old fifth-grade elementary school student affiliated with the Sirius theatrical troupe. Despite her youth, she possesses overwhelming acting ability that allows her to instantly dominate the stage and currently stands as Sirius's sole Dai Star candidate. Her talent coexists with significant potential for growth, fueled by stoic dedication to practice and refining her craft.

Described as angel-like in demeanor, Yae typically treats everyone with politeness and respect. This contrasts with Hiiragi Noa's observation that Yae possesses a selfish side, revealing a more complex personality beneath her courteous exterior. She identifies herself using the four-character idiom "初志貫徹" (shoshi kantetsu), meaning "to follow through on one's first wish." When comparing herself to an animal, she selects a hamster.

Her personal interests include developing cleaning tools and maintaining tidiness, skills she lists confidently alongside acting. She enjoys making omelette rice and eating traditional breakfast dishes like ozoni. Yae prefers spring for its warmth and daytime for its brightness. Her ideal day off involves volunteer work, and she would donate lottery winnings rather than spend them personally. She states a wish to be reborn as a god if given the choice.

In interpersonal dynamics, Yae consistently shows a strong preference for interactions with Sirius's vice-president, Hiiragi Noa. She selects Hiiragi as her choice for a hypothetical troupe date and wishes to attend another troupe's play exclusively with her. Yae also references Hiiragi's assessment of her personality when discussing others' first impressions versus her true self.

Professionally, Yae cites Maurice Maeterlinck's "The Blue Bird" as her favorite theatrical work. Her fundamental motivation is wanting to make everyone happy through performance, a commitment she promises fans to fulfill. Her latest significant purchase was a set of poetry books.