Hotaru Kurenai is a senior at Otogi High School, recognized by her medium-length hair and frequent use of headphones around her neck. Her calm and friendly demeanor pairs with a keen interest in romance, while she aspires to become a singer yet repeatedly considers pursuing comedy.

Before high school, she met Kaguya Gekkou when Kaguya assisted her in preparing for a mathematics entrance exam by predicting questions based on historical patterns. This sparked an enduring friendship where Hotaru manages Kaguya's quirks—such as avoiding school—and admires her intellect. Kaguya supports Hotaru's dream of becoming a YouTuber.

During a shared programming class, Hotaru interacts with Nasa Yuzaki, questioning his marital status. Later, she seeks his advice about her boyfriend's preoccupation with video games and anime, which leaves her feeling neglected. She also delivers a mathematical note from Kaguya to Nasa.

Her activities include attending supplementary lessons at Nasa’s bathhouse residence, though the session shifts into a heat endurance contest. She participates in a low-budget horror film project with the film research club, inviting Nasa and others to a ghost house. There, she encounters a fabricated ghost and flees a centipede-like monster before being rescued.

After viewing an M1 Grand Prix trailer, she voices interest in stand-up comedy, drawing skepticism from peer Inukai Hakase. At a karaoke event, she initiates a singing contest and suggests Tsukasa use the venue’s cosplay service, leading to Nasa selecting a princess costume.

Beyond Kaguya, she maintains friendships with Nikotama Jessie and other Otogi High students, regularly joining them in group activities and school events.