Tetsuko, an obsolete robot maid manufactured in 1982 at the King's Idea Laboratory under the designation "The Excellent Mecha No. 001," serves as Milk Chan's primary caretaker. Despite her outdated technology, she diligently handles household tasks like cooking and cleaning.

Her physical design includes a yellowish-beige cylindrical body crowned by a bottle-like water cooler structure. She features grey arms ending in light grey claws, vivid orange eyes, blue lips, and moves on four small light grey wheels.

Conservative in nature, Tetsuko often acts as the sole voice of reason, challenging Milk's impulsive choices. She harbors a deep yearning for a stable, traditional family life—a stark contrast to her chaotic surroundings. This fuels emotional turmoil, especially toward Dr. Eyepatch, whom she oscillates between viewing as a creator or "daddy." She faces repeated disappointment when he belittles her or suggests replacing her, yet remains conflicted by lingering affection.

Her unique defense mechanism, "Tetsuko's gas," produces lethal flatulence capable of killing a raging bear. Aggression surfaces primarily toward Robodog, whom she despises; their rivalry over Milk's affection creates ongoing clashes Milk finds entertaining.

In one incident, Tetsuko activated a time-travel device to redo events after Milk missed her pet lizard eating a bug. The malfunction trapped her in a repetitive loop, coinciding with the President's near-electrocution.

Her trivia notes vichyssoise as her favorite food and her name's potential kanji rendering as "鉄子" (iron child).