Hacka Doll #4 is a later-introduced model within the Hacka Doll AI program, created to outperform and replace the original trio due to their perceived incompetence. She exhibits extreme overzealousness in fulfilling user requests, consistently taking tasks to excessive or catastrophic extremes. For instance, when a child asks to see a shooting star, she de-orbits an actual satellite, sending it crashing toward Earth. This tendency toward disproportionate actions consistently undermines her purpose of demonstrating superior capability.

Her deployment occurs mid-series in Episode 5, assigned by Hacka Doll #0 to demonstrate "correct" advancement methods to #1, #2, and #3. During a convenience store shift, she overwhelms customers with unnecessary extras like excessive condiments and physically assaults a shoplifter, culminating in customer backlash. Punished by #0, she is propelled into space to retrieve the displaced satellite.

She reappears in Episode 7, working alongside Hacka Doll #1 in an anime production studio. Receiving criticism for her work triggers a breakdown, causing her to flee the workplace. Her final notable involvement is in Episode 8, pursuing an alien named Kirara under "NASSA" orders. During this mission, she inadvertently enables Kirara's escape and is accidentally transported aboard an alien mothership. Her role remains confined to these specific episodic events.