Kantarō Okuyama is a young man recruited into Hijikata Toshizō's group during the pursuit of the Ainu gold. He was born in Sapporo on the island of Hokkaido. Kantarō is in his early twenties and has an average appearance, characterized by dark eyes and dark hair that is tied back. His thick eyebrows and dark lower lids are defining features of his face. He is often seen wearing a happi coat, a traditional Japanese coat, over a mandarin-collared shirt. This coat originally bore the name of the Hidoro family, indicating his former allegiance to them as a bodyguard. Later, after a significant battle, his happi is shown with his own name, Okuyama, signifying his break from that past association.

In a story filled with eccentric and larger-than-life characters, Kantarō is noted for being relatively ordinary by comparison. Despite this, he possesses a strong desire to prove himself and to forge his own identity as an individual. As a former bodyguard for the Hidoro family, he has practical combat experience and is proficient with a Type 26 revolver as well as an Arisaka Type 30 rifle. He is involved in the hunt for the escaped convict Jack the Ripper, during which he dons a vendor disguise. In this confrontation, Jack the Ripper cuts Kantarō on the forehead, a wound that leaves him wearing a bandage for the remainder of the search for gold. After the Battle of Hakodate, he is seen with the bandage removed.