Rokuzō was a boy in his early teens. He had shortly cropped, brown hair and brownish-gold eyes. He wore a light blue button-up under a thick, white knitted sweater with the sleeves pushed up. He donned a brown bracelet on his left wrist.
His attire consisted of tightly fitting, dark green pants with the right pant leg partially rolled up. He had white high top sneakers.
An impatient and intelligent young boy, Rokuzō held disdain towards anyone who wasted his time, especially when it came to working. He strongly resented Doppo Kunikida's involvement in his life, associating him and the Azure King with his father's death. However, he was not uncooperative towards him, going as far as to agree to dig information about the Azure Messenger and serial kidnappings in Yokohama.
When he learned the culprit of the kidnappings was his father's killer’s lover, he didn't hesitate to shoot and kill her.
Rokuzō had no supernatural ability but was highly proficient with hacking into computers and gathering information.
Rokuzō's father was murdered by the Azure King. Feeling heavy responsibility for the boy's well-being, Kunikida took to providing him with appropriate living accommodations and resources. Living alone, Rokuzō developed proficient hacking and informational skills.
After receiving an anonymous tip about some kidnapping cases, Kunikida along with Dazai and Atsushi went to speak with Rokuzō. He found being a bit late unusual and wondered if he was on a date, but Kunikida brought out his Ideal and that dates should be with a chosen woman, who he will marry after six years. Seeing the new guy, Atsushi, Rokuzō introduced himself and revealed he can find any dirt about someone for the right price. Rokuzō then explained the tip was from Azure Messenger and that he also found some pictures of the kidnapped people on the server. Rokuzō assumed the tipper wasn't a bad guy, but Dazai wondered about that, hoping that the tipper won't turn out to be one of the kidnappers. Kunikida wanted Rokuzō to keep looking for information about the tipper and then they left.
Upon learning about the bomb, Kunikida called Rokuzō on the next day and asked him to try to dig some information about the bomb equipment they found. Later Rokuzō called Kunikida informing him that recently someone brought transmitter and other equipment to be delivered to a former defense facility. Rokuzō later hacked Dazai's email and went to the abandoned hospital, where Dazai had called the culprit to come. Upon arriving there, Kunikida thought Rokuzō was the culprit, but Dazai explained he likely hacked his email. Nobuko then came and shot Rokuzō, revealing that she was the culprit and that the Azure King was her boyfriend. As Dazai couldn't shoot her, he dropped his gun and the dying Rokuzō picked up and shot her.
- Rokuzō owned tropical fish that he kept in a tank.
- Rokuzō is named after the important character in Doppo Kunikida's romantic work "Spring Birds".