Sarah appears as a mysterious non-player character within the virtual reality game Gunpla Battle Nexus Online (GBN), encountered by protagonists Riku and Yukio. She exhibits unusual sensitivity to Gunpla, often accompanying Riku without ever piloting her own model. GBN's system later identifies her as an "EL-Diver"—an electronic lifeform spontaneously generated within the network from the accumulated emotions and consciousness surrounding Gunpla, confirmed by the absence of human registration data.

During a conflict involving Mass-Divers using illicit modifications, Sarah faces existential threats, including potential erasure during the second Coalition of Volunteers battle. She is protected by Riku and the Build Divers force. Following this crisis, her consciousness and data are permanently transferred into a custom-built Gunpla body designated the HER-SELF Mobile Doll Sarah. This form enables interaction in the real world while retaining her ability to log into GBN as a standard user.

As the first identified EL-Diver in GBN, Sarah's existence suggests a wider emergence of digital lifeforms. Her color scheme and design elements embody a legacy connected to earlier or related entities within the system. After stabilization, she maintains peaceful interactions with the Build Divers across both physical and virtual environments.

Sarah subsequently appears in later continuities, including the *Gundam Build Divers Re:RISE* series and the anniversary special *Gundam Build Metaverse*, confirming her enduring presence within the franchise's interconnected narratives.