Nagumo has a considerably short temper, to a point where he's willing to fight Kiryu for seemingly trivial reasons, before considering him a brotherly figure. He 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 secret of Onomichi, Toru Hirose adopted him and Matsunaga, taking care of them. At some point, he met Yuta Usami and Naoto Tagashira 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 develop a crush on her. He became a customer in her bar and would frequently visit her.
When Kazuma Kiryu arrives with Haruto Sawamura in Onomichi, Kiyomi invites him into the bar. Jealous of Kiryu, Nagumo challenges him to a fight outside the bar, and is 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.
He develops a rivalry with Kiryu, getting into another fight at a baseball field and having Yuta and Takaaki Matsunaga help him, but are all beaten. After a third fight outside the bar, Kiryu goes back in and Nagumo is beaten up by the Masuzoe Family for Nagumo's tardiness with his collections. Kiyomi tries to give her money to Nagumo, but he refuses. This results in Koji Masuzoe dragging him outside and continuing his beating. Suddenly, Kiryu comes to Nagumo's rescue and takes down Masuzoe and his goons. Kiryu explains that he helped Nagumo because he was impressed that he stands up to his principle and stays strong in front of the woman he loves. This changes Nagumo's perception of Kiryu, and he comes to respect Kiryu as an "aniki."
Nagumo introduces Kiryu to the Hirose Family, and Matsunaga argues with Nagumo for ruining their reputation, which caused the former's customers to make fun of him. Nagumo apologizes to Kiryu for his friends' bad manners and tells him that he's welcomed here anytime. The next day, when Kiryu comes to ask him and the others about Haruka Sawamura, they all poorly hide the fact they know her. Later that night, he tells Kiryu everything he knows: when Kiryu showed him her photo, Nagumo finally found out about his real identity as the fourth chairman of the Tojo Clan. He tells Kiryu about how people of Onomichi had taken a liking to her and had been protecting her during her time in Hiroshima. Nagumo also reveals that Haruka had been working at Kiyomi's bar when she was in town.
The next day, he finds out that Kiyomi has a relationship with Takumi Someya of the Tojo Clan, and becomes totally shocked. Ino comes in and informs them that Kiyomi has been kidnapped by yakuza, who are working for Someya, and he is having a negotiation with the Yomei Alliance at a hotel. They decide to raid the hotel and Hirose shows up and provides them with masks in order to conceal their identities.
They attack later, and after taking out the goons in the bathroom, Nagumo accidentally takes off his mask because he's feeling too hot. This causes Masuzoe to recognize him, blowing their cover. After Kiryu's battle with Someya, he finds out that Someya had married Kiyomi, and is stricken in grief. Kanji Koshimizu, the captain of the Yomei Alliance, attempts to exile the Hirose Family for their actions, but the Yomei chairman, Heizo Iwami, tells Koshimizu to spare them.
After the raid at the hotel, Nagumo still feels depressed, because Kiyomi has not only married Someya, but also had a child. He also finds out that their former friend, Shu Tatsukawa, is suspected to be Haruto's father from Kiyomi's testimony. When Kiryu decides to return to Kamurocho in order to locate Tatsukawa, Nagumo and Yuta decide to accompany him, with Nagumo apparently still upset because of Kiyomi's relationship with Someya.
When they arrive at Kamurocho, they search for leads regarding Tatsukawa, leading to them being assaulted by the Jingweon Mafia. Nagumo holds them off, and after Kiryu and Yuta gain information from Jingweon leader Joon-gi Han, they go into the apartment where Tatsukawa lives, only to find out that he has been brutally murdered, along with an unknown woman. Nagumo, Yuta, and Kiryu team with with Shun Akiyama to infiltrate Little Asia to learn about Tatsukawa's death, and fight the Saio Triad. They are cornered by Masuzoe - secretly loyal to the Saio - and Ed, but the leader Big Lo orders them to be spared.
Kiryu, Nagumo, and Yuta return to Onomichi when they learn Hirose had kidnapped Haruto and disappeared. Kiyomi tells them what had happened and, when informed of Someya, laments her failure as a mother with her daughter, but Nagumo is quick to reassure her. During their search for Hirose, Nagumo knocks out Koshimizu with a bottle during his fight against Kiryu and are led to Ryunan Shrine, where Hirose waited. They learn Yuta was Haruto's real father and Nagumo is quick to reprimand him. Masuzoe enters and informs them Yuta was also the secret heir to the Saio Triad, and the Jingweon stage an assault. Nagumo and the Hirose family try to keep Haruto safe, but are unable to do so.
Ino prepares a ship and Nagumo retrieves Kiryu and Yuta, though the latter needed some convincing from Kiryu to join. They head to an abandoned cargo storage site and fight their way through the Jingweon, with Kiryu succeeding in retrieving Haruto. Kiryu and Yuta leave for Kamurocho to resolve matters the next day.
When Kiryu returns, Nagumo, Tagashira, and Matsunaga fight him for accusing Hirose of being involved in a conspiracy. After beating them and investigating, they follow the trail of the Secret of Onomichi and Nagumo sees Hirose attempt to kill Kiryu. Nagumo shields him after the Yamato Mark II is reveals, and Hirose is unable to kill him, causing him to be shot by Heizo Iwami, who reveals Hirose's involvement. With his dying breaths, Hirose admits to his murder of their fathers.
After mourning Hirose's death the next day, they fight the Tojo Clan and the Yomei Alliance in Onomichi and then in Kamurocho, joined by Akiyama. Nagumo reaches the top floor of the Millennium Tower to witness Someya sacrifice himself for Kiyomi, and having that sacrifice be in vain. Someya entrusts their daughter to Nagumo. Nagumo and Kiryu decide to continue the fight alone. They head to Onomichi and reach the masterminds Tsuneo Iwami and Katsumi Sugai, but are forced to stand down because Haruka and Haruto are held hostage. Yuta, Matsunaga, and Tagashira arrive to save them, and after the Tsuneo's defeat, Nagumo tries to disarm Sugai, but in shot in the leg. He witnesses Sugai wound Kiryu, but the former kills himself with his last remaining bullet.
One month later, Nagumo meets with Hiromi and Kiyomi, previously thought to have died. With Yuta leaving to live with Haruka and Haruto; Nagumo, Matsunaga, and Tagashira aim to rebuild the Yomei Alliance, with Nagumo taking over as patriarch of the Hirose Family.
Team Heat Action w/ Kiryu
When Kiryu grabs an opponent while standing near Nagumo, and the player presses the Heat action button, the Nagumo 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.
- He shares his voice actor with Tsuyoshi Kanda. The two also have the same first name phonetically, which makes the names look identical in translation, but the "Tsuyoshi" in their names are written with different kanji characters in Japanese.
- Like Yuta Usami, he is voiced by someone who previously voiced a Yakuza 3 character.