Buku serves as Etsuko Sarutobi (Ecchan)'s primary talking animal companion. He speaks human language but cannot normally communicate with other dogs, a limitation highlighted in multiple episodes, except for one documented instance where he temporarily bridged this gap. His personality shifts between childlike playfulness and the role of a mature advisor to Ecchan as situations demand. As Ecchan's loyal partner, he accompanies her when she transfers to a new elementary school and moves in with her friend Miko's family following Ecchan's memory loss. Buku joins Ecchan's adventures, collaborating to resolve challenges. Specific episodes focus on him, including "Where Is Buku?/The Happy Couple," depicting a search after his disappearance, and "Buku and Chibimaru," detailing his interaction with another dog. His role extends to educational contexts, such as the episode "My Animal Language Classroom." Beyond the main series, Buku appears with Ecchan in the *Genma Wars REBIRTH* manga as part of the esper army cast. His character lacks significant development or a detailed backstory across official media. His portrayal remains undocumented in movies, OVAs, or spin-offs, and no concrete information exists regarding his origin or breed beyond being Ecchan's canine companion.