Jill manifests as an incarnation of Eve within a particular book world, serving as an assistant caretaker at an orphanage. Mute, she communicates solely through gestures and facial expressions. Her focus centers on nurturing the children under her care, especially young orphans Gargantua and Ritsuko, using her healing abilities to aid others. This nurturing fosters intense devotion and possessiveness in Gargantua.

A pivotal moment arises when Gargantua, consumed by jealousy over Jill's equal affection toward Ritsuko, attempts to forcibly separate them. During the struggle, he accidentally stabs Jill. This fatal injury occurs on her sixteenth birthday, triggering her dissolution into green souma energy. Her physical form vanishes in an explosion of this energy, drenching Gargantua and Ritsuko and granting them immortality. This event profoundly shapes their subsequent psychological states and actions.

Jill's death establishes core motivations for others: Gargantua's descent into obsessive vengeance and Ritsuko's century-long quest for meaning. Her role as catalyst stems directly from her identity as a manifestation of Eve, bound by Eve’s cyclical existence across worlds. Her presence or development in other book worlds, spin-offs, or alternative media remains unaddressed beyond this narrative arc.