Shirayuki Rei is the reliable member of drop, and also An's roommate and close friend. As he is the most reliable one in the unit, Rei and An share the role of leader together. Rei likes to be useful to other people, and is often seen helping students and teachers around the school. He is also often described as gentle and kind, but Rei himself thinks otherwise and would call himself someone who lacks a heart and feelings. This is due to his inability to shed tears, as he says that he has never cried even once for as long as he remembers. Because of this, Rei admires and is jealous of his fellow unit member, Sairi, who can freely cry and express himself better than Rei.

Prior to joining Hoseki Gaoka, Rei lived alone with his mother, who always came home late due to work, leaving Rei alone at home. While waiting for his mother to come home, Rei often spent his time watching anime that aired on the TV--which would later become his reason to enroll in Hoseki Gaoka. He believed that if he were able to become a seiyuu, he might be able to express himself better.

Rei likes cats due to their carefree nature and occasionally visits cat cafes to enjoy the company of the cats there, and he even keeps a giant cat plush in his (and An's) room.