Kaoruko Yamada is a supporting character known for being the ever-present assistant and companion to Renko Kamishakuji. Her primary role is tied directly to Renko, as she is almost always at Renko’s side, helping with various tasks and inventions. She has black hair that is roughly shoulder-length and brown eyes, and she is often depicted wearing glasses and a school uniform.

In terms of personality, Kaoruko is relentlessly upbeat and cheerful, a stark contrast to Renko’s more serious and aloof demeanor. She frequently attempts to act as a buffer for Renko, trying to smooth over her companion’s sharp temper and put her outbursts into more tactful or gentle terms. Despite her good-natured efforts, this attitude often puts her at odds with Renko, resulting in her receiving a fair amount of verbal or physical abuse whenever her approach conflicts with Renko's serious nature.

Kaoruko plays a significant role in Renko’s various projects. She figures heavily in a wide array of inventions, frequently serving as a key component or the functional "brains" of whatever device has been created for a particular occasion. This close integration with machinery is explained by a central aspect of her character: Kaoruko is later revealed to be an android. This explains not only her ability to interface seamlessly with Renko's other inventions but also her logical and unflappable demeanor in many situations. As an android, she has also demonstrated notable combat abilities, such as piloting a dendrobium mecha with enough power to defeat two F-15 fighter jets, though she was ultimately shot down by another character. Her key relationship is overwhelmingly with Renko, defined by a dynamic where she serves as both an assistant and a frequent target of Renko's temper while remaining unfailingly loyal and present.