Banzaburo was a man of average size. His purple hair was parted into a puffy, pompadour-like shape to the right, and was also tied into a topknot at the back. On his face he wore a pair of orange-tinted glasses as well as small hoop earrings. He wore a navy blue kimono with a light blue vest over it; the vest had the Kozuki Family logo on both sides of its chest area. Forty-one years ago he had two small patches of hair on his upper lip; 21 years later, these had grown into a full beard. In the anime, he looks identical between both time periods.
Banzaburo was extremely loyal to the Kozuki Family due to Kozuki Sukiyaki taking him in as a youth. During Oden's life, Banzaburo greatly idolized the samurai's exploits and grew excited when recounting them to Sukiyaki, even as the shogun was less than enthused. Banzaburo remained loyal to the Kozuki Family after they lost their power and put his life on the line to serve and protect them, including doing things like tasting their food to check if it had been poisoned; he ultimately gave up his life defending the family when their castle was attacked by Kaidou.
Forty-one years before the present day, Banzaburo gave a report to Sukiyaki in the shogun's castle about his son, Kozuki Oden, trying and failing to illegally leave Wano 38 times. He then recounted the many outrageous exploits that the 18-year-old Oden had committed since he was born. In response, Sukiyaki told Banzaburo to give Oden a piece of paper to inform him that he was being disowned. Banzaburo reached Oden right as the young samurai had just saved the Flower Capital from an attack by the Mountain God, and said it pained him to give the notice of his disownment at this moment, but did so without fail.
When Sukiyaki died 25 to 28 years ago and Kurozumi Orochi succeeded him as shogun, Banzaburo left the service of the shogun in favor of serving Oden's family. 20 years before the present day, Banzaburo was seen with Oden's wife Toki and children Momonosuke and Hiyori while Oden and his retainers went to battle against Orochi and Kaidou, and he tested their food to make sure it had not been poisoned. Later, Banzaburo received word that Oden had been killed and reported this to Toki. Kaidou and the Beasts Pirates then attacked Kuri Castle and burned it down, killing Banzaburo, the other servants, and Toki.
- One Piece Manga and Anime — Vol. 95 Chapter 960 and Episode 960, Banzaburo makes his debut.
- SBS One Piece Manga — Vol. 98 (p. 174), Banzaburo's name is given.
- One Piece Manga — Vol. 96 Chapter 971.
- One Piece Anime — Episode 972.
- One Piece Manga — Vol. 96 Chapter 973.
- One Piece Manga and Anime — Vol. 95 Chapter 961 and Episode 961.
- One Piece Manga — Vol. 95 Chapter 962.
- One Piece Manga — Vol. 96 Chapter 972.