Chiku-tan is a young girl and a resident of the same rural, gentle world as the main character, Bincho-tan. She lives with her younger sister, Chiku-rin, and their grandfather, Madake, in an old house situated outside of town, similar in its seclusion to Bincho-tan's own home. Her name is derived from takesumi, the Japanese word for bamboo charcoal, connecting her to the series' theme of characters personifying types of charcoal. Her birthday is on August 24.

Chiku-tan has a bright and enthusiastic personality, approaching life with a cheerful and energetic disposition that makes her a Genki Girl type of character. She is defined by her boundless curiosity and a strong desire to help others, which is most prominently expressed through her hobby and passion for inventing things. Chiku-tan is a budding inventor who constantly tinkers and creates various contraptions intended to solve everyday problems or make life easier for herself and those around her. A distinctive physical trait accompanies this inventive drive: her hair is fastened with a piece of bamboo charcoal, and the end of this hair moves or vibrates whenever she gets an idea for a new invention or is pondering a solution to a problem. Despite her enthusiasm, her inventions often prove to be impractical, prone to breaking, or are sometimes merely reinventions of existing items, such as her "chikuma" walking device which was already known as a "takeuma". Nevertheless, she remains undeterred by these small failures and continually works on new creations with a persistent and optimistic spirit. An example of her handiwork is a portable house, though it also ends up breaking. Her curiosity extends to her surroundings, and she is always trying to get to the bottom of things she does not understand.

Chiku-tan's role in the story is primarily as the first and best friend of the protagonist, Bincho-tan. They meet when Bincho-tan falls and injures her knee, and Chiku-tan, being the granddaughter of an apothecary, uses her knowledge and supplies to tend to the wound. Following this initial encounter, their paths cross frequently as both often go to town to seek work, and they quickly become close friends. Chiku-tan is also responsible for introducing Bincho-tan to her family, culminating in a surprise birthday party for Bincho-tan at her house. A significant development in their friendship is their joint decision to adopt and raise a dog together, whom they name Saji. Beyond her relationship with Bincho-tan, Chiku-tan shares a close bond with her younger sister, Chiku-rin, and her grandfather. She also interacts with other characters in the community, such as Ren-tan, a mysterious girl who lives at a local temple. One of Chiku-tan's known fears is of ghosts, which leads to a comical situation when she mistakes Ren-tan for a ghost and becomes terrified. She also takes on various small jobs in town, similar to Bincho-tan, and on one occasion tries to sell her grandfather's medicine on the street with the help of Ren-tan.

Throughout the series, Chiku-tan's character shows development in her deepening friendship with Bincho-tan and her consistent, good-natured efforts to contribute to her community. Her motivations are simple and kind-hearted: she is driven by a genuine wish to be helpful, to solve problems, and to earn a living to support herself and her family. Her primary ability is her inventive ingenuity, even if the results are not always successful. She also possesses practical knowledge of medicines and first aid, a skill learned from her grandfather. Her expressive hair serves as a unique and prominent quirk, acting as a physical indicator of her creative thoughts.