Tetsuko, whose name probably translates to "steel child", is just that - friendly and gentle almost to a fault, but just hard enough to withstand the abuse hurled her. Milk always makes demands to Tetsuko, doesn't follow the sensible advice she gives her, and always calls her names. Nevertheless Tetsuko is loyal to Milk.
Tetsuko was made at the Kings Idea Laboratory, and everytime she visits she hopes that she'll meet her maker, whom she refers to as her father. What she gets every time is an encounter with Dr. Eyepatch, who never gives up the chance to hurl abuse at her, leaving Tetsuko hoping that Eyepatch isn't her father.
The only character that brings out Tetsuko's aggressive side is Robodog, whom she hates. They are in a constant battle for Milk's affections, to Milk's amusement.