Riku Rei, alias Rei Riku, is a pink-haired, red-eyed high school student whose life intertwines with virtual realms as the adopted daughter of Yuuki Riku, creator of the online RPG *Dungeon Century*. Her fate becomes pivotal in the tomb-raiding game *Grave Buster* after she rescues the protagonist from a near-drowning, forging a bond that transcends their initial anonymous interactions within *Dungeon Century*. When the game shuts down, her abduction propels the protagonist into *Grave Buster*’s depths, unraveling mysteries tied to his past and her cryptic link to the enigmatic entity known as “The Collector”—a connection hinted by their striking resemblance and shared voice. As both a catalyst and a bridge between realities, Rei’s adoption and hidden role in the games’ development anchor her at the nexus of intertwined virtual and personal histories.