Atl, an Aztec girl from Mexico orphaned in Texas, desperately prayed to Quetzalcoatl. This summoned a supernatural Youi in the form of a massive horse, which she named Yukiwa (also called Quetzl). This Youi could transform into a dragon. Inspired by tales from shipwrecked samurai, Atl sought refuge in Japan.

As a foreigner with bronze skin facing intense prejudice in Edo-period Japan, she artificially lightened her skin with makeup to hide her heritage. She initially performed with Yukiwa in a traveling circus. After her true identity was exposed, leading to ostracization, Genbatsu arranged for her care under geishas in the red-light district; she did not become a geisha.

Atl uniquely perceives Kumoshichi, a Youi usually invisible except to Ryūdō Yukiatsu, correctly identifying him despite his human guise. She formed a protective, quasi-familial bond with Yukiatsu, rooted in their shared experience as outsiders resisting the Other World. During Quetzl's uncontrollable rampage, Kumoshichi merged with the horse, stabilizing it and creating a sentient, talking Quetzl with Kumoshichi's consciousness preserved.

Her presence ties into a stable time loop, as Atl and other Ayashi members were instrumental in aiding the young Yukiatsu's return from the Other World to the human realm in the past, facilitated through their future actions.

Depicted as a teenage girl with green eyes, brown hair in a chest-length ponytail secured by a ribbon, and tanned skin, Atl is often seen wearing a yukata. Her background exemplifies themes of cultural displacement, resilience against societal rejection, and the search for belonging.