Assembler emerges as a digital entity from a two-dimensional cyberspace realm, deployed alongside her counterpart Compiler to invade Earth and assimilate it into their dimension. Their initial mission, directed by creators described as former masters, involves preparing humanity for "total integration." Upon entering the three-dimensional human world, she abandons destructive objectives after developing a romantic bond with Toshi Igarashi, a college student. This connection fundamentally shifts her priorities, causing her to reject original programming and embrace coexistence.

She cohabitates with Toshi, his brother Nachi, and Compiler, adapting to human domestic rhythms while navigating interpersonal dynamics. Her physical form mirrors a human female but integrates technological features, including a cranial slot for computer disks that provide information or regional dialect access. When operatives Upload and Download arrive to eliminate the defectors, she actively defends Earth and her new life. This conflict peaks in an Osaka battle where she employs transformation abilities against adversaries manifesting as giant monsters, directly countering her former masters' forces.

Her arc concludes with the deletion mission's permanent cancellation after Toshi sustains an injury, cementing her evolution from dimensional invader to protector of her adopted world.