Chako is a robotic cat abandoned by her previous owner and destined for disposal in a smelter until rescued and rebuilt by Luna's father. He then gifted Chako to Luna, who initially disliked her. Over time, recognizing shared experiences, Luna developed a bond with her.

Chako covertly boarded the spacecraft during a school field trip, resulting in her presence when the group became stranded. On the uninhabited planet, she provided essential technical assistance, frequently collaborating with Shingo to overcome electronic and mechanical challenges. Functionally, Chako requires sustenance, breaking down sugar from food—particularly fruit—to generate energy. Her specialized sensors enable environmental analysis, medical diagnostics, and identification of edible substances.

She possesses extendable claws, though these serve no practical combat function. The name "Chako" was reluctantly accepted after Luna, distressed following her mother's death, proposed it during their early, strained relationship.