Sayless, alternatively spelled Seres, emerges as a pivotal entity from the fantasy realm Dela Grante. She stands as the most recent incarnation in an ancient priestess bloodline, fated to avert a planetary catastrophe. Her physical traits include blonde hair and distinctively pointed elf-like ears, while her muteness necessitates non-verbal communication.

Following the demise of the knight Illia, who previously guided protagonist Takuya Arima, Sayless assumes the role of Takuya's foremost companion. Their bond deepens into romance, culminating in the birth of their daughter Yu-no. Sayless fulfills maternal duties for Yu-no, who later inherits her position as the reigning priestess.

Confronted by Imperial Capital knights during Takuya's temporary absence, Sayless chooses suicide to evade capture. Her death method differs across adaptations: self-inflicted knife wounds in the anime versus tongue severance in the original visual novel. This sacrifice ignites Takuya's mission to rescue Yu-no.

Though deceased, Sayless's influence endures through Yu-no. Her priestess heritage connects directly to the core conflict—a ritual sacrifice mandated to prevent the cataclysmic collision of Dela Grante and Earth. Additionally, she is disclosed as Takuya's eventual spouse within his original timeline.