Rikei Hiromatsu attends Ebisugawa High School as a second-year student and belongs to the Astronomical Club. She maintains a consistently quiet and emotionless demeanor, typically following instructions without resistance and appearing detached from surrounding events. Her interactions reveal a distinct interest in cats, bordering on a fetish; contact with cats elicits rare displays of emotional responsiveness, breaking her usual stoicism. This cat-related enthusiasm manifests as a focused fascination, temporarily displacing her passive disposition. She wears the standard school uniform with stockings, sports a neck-length blonde side ponytail featuring a flower accessory, and has blue eyes.