Ruri Hayasaka, known to friends as "Ruri-Ruri," is Ichika Mizuhara's friend who shares Ichika's view of Tomoya Mizuhara's adorability. She presents a consistently sweet and gentle demeanor among friends, appearing incapable of wrongdoing. This amiable facade starkly contrasts with her behavior toward her younger brother, Kouki Hayasaka. Ruri exerts complete dominance over Kouki, regularly subjecting him to physical control through headlocks and other harsh punishments. She imposes these measures both in response to actual misbehavior and on mere suspicion of wrongdoing, establishing a pattern of abusive conduct within their sibling relationship.

Kouki Hayasaka, identified as Ruri's younger brother, maintains high academic standing yet lives under her oppressive control. Despite enduring Ruri's consistent harsh treatment, Kouki secretly harbors romantic feelings for her, infusing their interactions with underlying tension.

Physically, Ruri possesses light blue hair and green eyes and is identified as a student.