Rei, also known as Ray, is a Siren Xenos and one of three leaders among her kind. She possesses golden feathers with blue tips, piercing blue eyes, and wears attire reminiscent of an Amazoness. Her beauty rivals that of the prominent Xenos Wiene. Rei displays a warm, friendly demeanor but unleashes intense bloodlust when sensing threats to the Xenos, driven by primal instincts to protect her kin. She cherishes her fellow Xenos and yearns for life on the surface—dreaming of flying in sunlight and being embraced by a loved one. Despite learning of Ranye's group's deaths and the capture of Wiene and Fear, she resisted the rage that consumed others. After encountering Bell Cranel and Welf Crozzo, Rei initially mistook them for Xenos hunters but recognized their divergence from typical adventurers, igniting hope for improved human-Xenos relations. She later hosted the Hestia Familia in the Xenos' Hidden Village, using her singing to soothe their spirits. During the Xenos' invasion of the 18th floor, Rei doubted Bell's loyalty but felt profound joy upon discovering his rescue of a Xenos. Witnessing his unwavering aid to her kind—despite personal repercussions—awakened romantic feelings within her. Rei wields standard Xenos abilities, including high-speed flight. As a Siren, she attacks with sound waves and utilizes echolocation. Her gifted singing voice calms listeners and sparks rumors among Orario's adventurers. Her speech is often fragmented or scattered.