Hotaru Shirakawa is a third-year student at Hamasaki High School, known for her childish and immature demeanor. She often displays airheaded and naive tendencies, occasionally referring to herself in the third person. Her favorite pastime is playing the piano.

Physically, she stands 158 cm tall with a slim build, brown eyes, and long brown hair styled in waist-length twin tails, spiky bangs, and an ahoge. She frequently wears her school uniform, miniskirts, thigh-high stockings, and ribbon hair accessories.

Her closest bond is with her best friend, Tomoe Tobise. Romantically involved with Ken Inami after confessing during Christmas, she frequently worries about his feelings despite their continuing relationship. Her older sister, Shizuru Shirakawa, shares a close relationship with her, spoiling her, making desserts she enjoys, and actively supporting her romantic concerns.

Beyond *Memories Off 2nd*, Hotaru appears in multiple franchise installments. She features in both OVA segments of *Memories Off 3.5*: *Omoide no Kanata e* and *Inori no Todoku Toki*. In *Memories Off ~Sorekara~*, she serves as a secondary character, guiding Inori Misasagi regarding her relationship with Isshu Sagisawa. These recurring appearances emphasize her ongoing connections within the series, often alongside Shizuru and the character Shin Inaho.

Her surname, Shirakawa, combines the Japanese words for "white" (白) and "river" (河). Her given name, Hotaru, written as 蛍, means "firefly".