Sumire Hikami joined Starlight Academy at her older sister Azusa's suggestion, seeking to become an idol despite her solitary nature. Entering with a competitive mindset, she initially saw fellow students as rivals, believing the idol world operated on a principle where one idol's success meant another's failure. This led her to practice primarily alone early on. Her reserved, polite, and soft-spoken demeanor, combined with an interest in fortune-telling and carrying tarot cards, characterized her initial interactions. She held a deep affinity for the gothic fashion brand LoLi GoThiC, influenced by her sister, and admired senior idol Yurika Tōdō as its ultimate stylist.

Significant development occurred when Sumire became roommates with Akari Ōzora. Akari's open friendliness, especially her willingness to invite Sumire to joint activities like auditioning to be Ichigo Hoshimiya's temporary manager despite viewing others as potential rivals, gradually softened Sumire's isolated outlook, fostering a shift towards valuing friendship and collaboration. Shared experiences, including Sumire overcoming her ichthyophobia (fear stemming from dead fish's soulless eyes) and supporting each other through auditions and performances, strengthened their bond. Sumire also formed meaningful connections within her class, notably evolving her formal interactions with Hinaki Shinjō into genuine friendship. These relationships culminated in forming the unit Luminas with Akari and Hinaki, symbolizing her integration into a supportive peer group.

Professionally, Sumire refined her elegant singing style, earning the nickname "Blooming Ice Flower of the Stage." She actively sought growth, such as obtaining the LoLi GoThiC Snow Princess Coord Premium Rare dress by proving her dedication to the brand's designer, Maya. Her partnership with Rin Kurosawa in the unit Dancing Diva proved pivotal; their complementary skills—Sumire's vocals and Rin's dance—fostered a sibling-like dynamic built on mutual support. Sumire framed their partnership with the declaration, "I will make you shine, and in exchange, I want you to make me shine as well." This collaboration honed her abilities, though she faced setbacks like a failed Special Appeal during a performance, highlighting idol challenges. Her journey involved balancing unit activities in Luminas and Dancing Diva while participating in larger events like the Starlight Queen Cup preparations during a nationwide tour.

In "Aikatsu! 10th Story ~Starway to the Future~," focusing on Ichigo Hoshimiya, Aoi Kiriya, and Ran Shibuki's post-Starlight paths, Sumire Hikami appears as part of the supporting cast alongside other established idols. The narrative centers on Ichigo's final year decisions and a successful duo performance with Akari Ōzora as "Cosmos," situating Sumire within the ongoing idol activities and relationships at Starlight Academy during this period.