Nagumo has a considerably short temper, to a point where he's willing to fight Kiryu just for seemingly trivial reasons, before considering him as a brotherly figure. He also has a high sense of loyalty to people he respects.
Nagumo wears a floral blue shirt, along with beige plaid pants, a maroon belly warmer and a pair of white shoes. He has short hair with an undercut, and a noticeable freckle on his left cheek. During his trip to Kamurocho with Kiryu, he wears a brighter blue floral button-up shirt with a black striped suit jacket over it along with striped suit pants, black shoes, and a gold chain.
After killing their fathers to protect the Onomichi secret, Toru Hirose adopted him and Matsunaga and took care of them. At some point, he met Yuta and Naoto and they formed a small clan known as "Hirose Family" with Nagumo as the second-in-command. The clan worked in a protection racket in extortion for protection money from various places under the supervisions of the Masuzoe family. Nagumo met Kiyomi with Ino in high school and eventually had a crush on her. He became a customer in her bar and would frequently visit her.
When Kazuma Kiryu arrives at Hiroshima, Kiyomi invites him into the bar. Nagumo obviously not pleased that he and the baby get all the attention while being scolded by Kiyomi for smoking near Haruto. Jealous of Kiryu, Nagumo challenges him for a fight outside the bar, and was defeated by Kiryu. Nagumo then warns Kiryu that he's the second-in-command of the Hirose Family and that he'll be back for revenge.
The day after that, he reappears with his friends, Yuuta and Matsunaga to pick a fight with Kiryu. But they're all ended up bickering among themselves and resulted in Kiryu to ignore them. Later in the baseball field, Nagumo and his friends revealed to be in the opposing baseball team. Nagumo once again feels jealous of seeing him with Kiyomi and challenges him for a match.
During the match, Nagumo purposely causing dead balls, which injures Kiryu's teammates. Kiryu then goes up for hitting. He dodges Nagumo's pitch and narrowly throws a bat at him. Nagumo then fights Kiryu again with the help of Yuuta and Matsunaga, but all three of them were defeated nonetheless.
That night, Nagumo reappears in Kiyomi's bar and once again asking Kiryu for a fight. After being defeated for the third time, Kiryu tells him to stop embarrassing himself and that he's not worth fighting. Shortly after Kiryu goes back into the bar, he was beaten up by the Masuzoe family who demands to know why Nagumo's late for bringing in the protection money. Kiyomi decided to give her money to Nagumo, but he refuses it; Telling her that if he accepts the money, he can never return to her bar as a customer anymore. This results in Masuzoe dragging him outside and beats him up some more.
Suddenly, Kiryu comes to Nagumo's rescue and take down Masuzoe and his goons. Kiryu explains that he helped Nagumo because he was impressed that he stands up to his principle and stay strong in from the woman she loved. This finally changed Nagumo's perception of Kiryu and he comes to respect him as a 'brother'.
Later, Nagumo introduces Kiryu to Hirose and they both chats for a while. Suddenly, Matsunaga arrives and calls Nagumo out. He reports that he picked a fight with a customer and Yuuta said that ever since Kiryu beat them in baseball, their reputation has been decreased lately. Nagumo tells Matsunaga to take the hits instead of fight back against the customers because it's not how they handle businesses. After the rest of Hirose family left to handle with the customers, Nagumo apologizes to Kiryu for his friends' bad manners and tells him that he's welcomed here anytime.
The next day, when Kiryu come and ask him and the others about Haruka, Nagumo becomes nervous and tried to avoid him. But later that night, he come and tells Kiryu everything he knows. When Kiryu showed him her photo, Nagumo finally finds out about his real identity as the fourth chairman of the Tojo Clan. He tells Kiryu about how the Hirose Family welcomes Haruka and being friendly with her as she is very kind and cute. The Hirose Family has been protecting her during her time in Hiroshima. Nagumo also reveals that Haruka has been working on Kiyomi's bar when she was in town.
The next day, he finds out that Kiyomi had a relationship with Takumi Someya of the Tojo Clan and become totally shocked. Ino suddenly comes in and inform them that Kiyomi has been kidnapped by Yakuzas. The Yakuzas are working for Someya and he was having a negotiation with the Yomei Federation at a hotel. Nagumo still determines to rescue her and went as far as trying to quit from the Hirose Family so that his family did not take the blame. His friends also want to assist him, but then Hirose shows up and decided to provide them with masks in order to conceal their faces so that no one could identify them. After planning their assault, he, alongsides Kiryu and his fellow family members attack the hotel to rescue Kiyomi.
After taking out the goons in the bathroom, Nagumo accidentally takes off his mask because he's feeling too hot. This caused Masuzoe, who happens to be there to recognize him, leading Kiryu to also have his cover blown. After Kiryu's battle with Someya, he finds out that Someya has married with Kiyomi and stricken in grief. Koshimizu, the captain of Yomei Federation attempts to exile the Hirose Family for their actions, but the Yomei Federation chairman, Heizo Iwami, who also goes by the name "Kurusu Takeru", tells Koshimizu to spare them.
After the raid at the hotel, Nagumo still feeling depressed because Kiyomi has not only married with Someya, but also had a child. He also finds out that their former friend, Tatsukawa, has been suspected to be the Haruto's father from Kiyomi's testimony. When Kiryu decided to return to Kamurocho in order to locate Tatsukawa, Nagumo and Yuuta decided to accompany him, with Nagumo apparently still sad and upset because of Kiyomi's relationship with Someya.
When they arrived at Kamurocho, Nagumo, Kiryu, and Yuta go to Cafe Alps in order to plan their search for Tatsukawa. They then go to Stardust in order to find him, but suddenly Yuta got a stomach ache. At the mini-market, Nagumo finds out that Daigo Dojima is going to go on penetentiary soon. Nagumo suspects that Someya would gain more power if Daigo stays behind bars. However, Kiryu couldn't do anything about it because he's no longer a member of the Tojo Clan. When they got to Stardust, the bouncer doesn't let them in and apparently, Yuya and Kazuki are no longer own it anymore. They met Yuya on the street and they went to Kanrai to eat. After discussing about his condition and Tatsukawa, the new owner of Stardust, Han-Joon Gi, appears and tells Nagumo and the others to meet him at Stardust. But on their way to the club, they got attacked by the remnants of Jingweon Mafia. The trio manges to defeat most of them, leaving Yuuta and Nagumo to fend off the Koreans while buying Kiryu time to escape.
After defeating all of the Jingweon members, Nagumo heads to Stardust to catch up with Yuuta and Kiryu, but apparently, he got lost and goes into the massage parlor instead. He then reunites with Kiryu and Yuuta after they dealt with Han-Joon Gi. They went into the apartment where Tatsukawa life, only to find out that he has been brutally murdered, along with an unknown woman.
Team Heat Action w/ Kiryu
When Kiryu grabs an opponent while standing near Nagumo and the player executes the Triangle button, the Nagumo's Team Heat will play. Kiryu will grab the opponent's arm with his left hand, and push the opponent down by the head with his right hand. Nagumo will rush at the opponent and cross his hands, delivering a cut to the opponent's neck, sending them away.
- He shares his voice actor with Tsuyoshi Kanda, as well as his first name.
- Like Yuta Usami, he is voiced by someone who previously voiced a Yakuza 3 character.