Nagamasa Azai is the last head of the Azai clan, Oichi's husband, and acclaimed father of the Three Azai Sisters. He is best known in fiction for betraying the Oda by allying with the Asakura's revolt against Nobunaga. Current findings by researchers suggests that Nagamasa never formalized his alliance with Nobunaga –even with the political marriage– meaning that the trauma and personal guilt he allegedly suffered for his betrayal may have never occurred.
He first appeared in the Samurai Warriors series as a unique non-playable character in its first entry. He became a playable character in Samurai Warriors 2. Fans voted him to twenty-eighth place in Gamecity's Sengoku Musou 3: Empires character popularity poll. For the Samurai Warriors 4 poll, he placed twenty-ninth. This counterpart shares a duet image song with his wife titled Tokoshie ni Saku Hana.
His Nobunaga's Ambition counterpart is fifty-third place in Gamecity's character popularity ranking for 2015. The Nobunaga no Yabou 201X poll for 4-star officers puts him in thirty-fifth place. He placed thirty-first in the Nobunaga no Yabou Taishi poll for most favorite father.
Nagamasa is the virtuous lord of Bizen and Odani Castle. In Samurai Warriors, he is supportive of his young wife and often apologizes for any grief he may cause her. During her lower path ending, he openly states his wish for her to not fight her own family. She replies that it is inevitable and runs away from his embrace. In Oichi's true ending, he also appears regretful for betraying his brother.
In the second game, he strongly believes in love and honor. When he is forced to betray Nobunaga, he becomes conflicted between honoring his family's trust with the Asakura and his alliance with the Oda clan. In a dream, he sees the possible scenario where he postulates on whether he should uphold love and honor by attacking Nobunaga at Anegawa and Mt. Usa. His hesitation leads to a final confrontation between them at Odani Castle, in which he slays his brother-in-law. Guilt-ridden by his actions, he asks Oichi to leave him for abandoning his beliefs. However, Oichi's support remains and he uses this momentum to defeat the remnants of the Oda army at Shizugatake. His dream ends with him as the undisputed leader of the land.
When he awakens, a soldier informs him that he is at Kanegasaki, moments before his pursuit of the fleeing Nobunaga. Thanks to his dream, he knows that Oichi will love him no matter what his actions. Chasing the Oda army, he decides to first fulfill his duty to the Asakura by capturing Nobunaga. When he is successful, Nagamasa stays true to his ties with the Oda clan and defeats the Asakura. After their victory, Oichi is worried about him betraying his ideals. Nagamasa assures her that he is fine as Oichi is the one he truly wants to protect.
His dream stage is a continuation of his story mode. Nagamasa becomes a trusted ally of Nobunaga and assists his lord's final unification of Japan. The battle takes place at Sekigahara against the Takeda-Uesugi-Date coalition. Despite cannon fire by Yukimura and overwhelming reinforcements led by Kanetsugu and his lord, the Oda-Azai force triumphs, making Nobunaga the grand unifier of Japan. Nobunaga continues to look forward to the youth's accomplishments.
Nagamasa appears in the Ascendancy scenario of Samurai Warriors: Katana where his betrayal of the Oda at Kanegasaki is revisited. If the player fails to reach Nobunaga in time during the sprinting sequence, they will face the Azai warlord as their opponent.
Samurai Warriors 3 has Nagamasa start as a neutral party from Omi Province. With Nobunaga on the threat of being attacked by Yoshimoto's larger army, Nagamasa decides to protect the Oda at Okehazama. Before the encounter, he has a chance meeting with Oichi and shares his dream to one day see the fields of battle peacefully blooming with flowers. After Yoshimoto's defeat, Nagamasa falls in love with Oichi and he marries her. To aid his wife and new brother-in-law, he helps besiege Inabayama Castle. Upon Hanbei's defeat, he and Oichi swear to work together for a land of happiness. In due time, Nagamasa receives a report that Nobunaga has invaded Echizen and is threatening the Asakura. Knowing that he is the only ally that Yoshikage can rely on, Nagamasa rides to the Asakura's rescue.
Even though he resists Nobunaga, he feels no hatred or regret towards his relative. Instead, Nagamasa only wants to end the war between them so they may have a country where everyone can smile once more without conflict. Winning Kanegasaki and Anegawa, Yoshikage eventually falls against Nobunaga's forces. Although he believes that he can achieve his dream, Nagamasa asks Oichi to return to the Oda for her own safety, which causes his wife great distress as she leaves. He then fights the Oda army at Odani Castle. Disarming Nobunaga in their final duel, he spares his brother-in-law's life and asks Nobunaga to take care of Oichi for him. Believing that Nobunaga will honor his wish, Nagamasa turns and leaves for the burning Odani Castle.
In Sengoku Musou 3: Empires, he continues his defiance towards the Oda during Nobunaga's story route, hoping to make them settle their differences with the Asakura to no avail.
Samurai Warriors 4 Nagamasa is introduced into the main narrative with his political marriage to Oichi. Nobunaga selected him since he requires a strong ally to assist the overwhelming odds against his march to the capital. While he attends a cherry blossom viewing after their victory, Nagamasa makes it clear that he respects his brother's capabilities as a hero of their age yet doesn't completely agree with his rulings. He fulfills his duties to the Oda to honor their alliance. When the Oda forces face a possible crisis against the Rokkaku forces, Nagamasa leads his troops to assist the defenses of Kannonji Castle. He befriends Mitsuhide during these encounters yet feels they cannot see eye-to-eye with one another.
Hisahide remembered his statements at the viewing and privately goads the Omi lord to fight for his unique ambitions. Nagamasa takes the bait, his justifications for betraying his alliance solidifying with Oichi's devotion to him. He vehemently defies his brother-in-law to fight for his vision of unification: a world in which everyone can enjoy happiness. Nagamasa feigns safe passage for Nobunaga against his Asakura allies before charging the Oda's flank. Nobunaga narrowly escapes his ploy at Kanegasaki, so the Omi lord continues to build his forces by colluding with the Asakura and Takeda. He plans for a coordinated strike on his brother at Anegawa. With the Takeda's unexpected holdup in the east and the Asakura's sudden withdraw, Nagamasa loses his momentum against Nobunaga.
The Oda chapter has Nagamasa then side with the multiple insurgents at Noda-Fukushima. He gambles his chances on sheer numbers and charges directly for Nobunaga's main camp. If Oichi is defeated before him, she is captured and Nagamasa changes course to rescue her. Otherwise, he perishes in battle.
The Kinki chapter has Nagamasa instead survive the collapse of the anti-Nobunaga coalition, yet their fall signals the end of Nagamasa's dream. The Takeda are unable to assist with Shingen's death and the Asakura are completely obliterated by the Oda. Although the enormous Oda army surrounds and sets fire to his feeble Odani Castle, Nagamasa refuses multiple appeals to surrender during the siege. The pre-rendered version of his final battle shows him dueling a pleading Hideyoshi before Nobunaga fatally stabs him from behind. He is last seen falling within the castle's flames. A lone burnt tree acts as a grave marker for him and his dream.
During Chronicles 3, he has his own hypothetical scenario, where he prevails against Nobunaga at Anegawa. Thanks to this power change, the roles between his clan and the Oda become reversed, and Nobunaga now serves him as vassal. Although he is able to pacify the western lords, Hisahide bands together with the Hōjō of the east and other discontent factions to start a rebellion.
Enraged by Nobunaga's death at the hands of the rebels, Nagamasa progressively grows more ruthless in his actions, leaving his wife and subordinates wondering if he will ever revert back to his old self.
If the Hōjō are negotiated with before the battle, Nobunaga will survive the battle, and Nagamasa opts to spare the rebels once more.
In Spirit of Sanada, he appears briefly with other discontent anti-Oda factions to try and strike the daimyō at Noda-Fukushima. After Shingen's death, the Azai progressively lose ground until he is finally cornered and killed at Ōdani.
Nagamasa's death, decision to fight a futile battle and his smiling visage within his burning castle all leave a significant mark to the young Chacha, who wonders what the strength her father had in his last moments.
In Warriors Orochi, Nagamasa leads an independent resistance force with Oichi and Gan Ning at Chen Cang. He and his forces are defeated by Cao Pi and ask for death in face of defeat. Cao Pi instead recruits them for his war against Orochi, promising that if death comes, it will be in battle against the Serpent King. In Wei's seventh Gaiden stage, Nagamasa is sent, along with Oichi and Gan Ning, to Nan Zhong to aid Tadakatsu's army.
Coming into the fray at Cao Cao's request, he reinforces Jiang Weiand Toshiie during their attack on Yamatai in Warriors Orochi 2. He, Oichi, and Yoshikage assist in the chase for Himiko and Da Ji. Though unsuccessful in capturing the youngest fugitive, Cao Cao congratulates their efforts. Nagamasa shares his dream mode with Kanetsugu and Ma Chao, as the righteous trio rescue peasants attacked by Kiyomori's army at Nan Zhong.
After Orochi's second defeat, Nagamasa traveled the dimensional world with his wife to create a land without conflict. During their journey, however, they were attacked by the serpent forces and Oichi is taken prisoner. Coerced to fight for her safety, Nagamasa regretfully faces Yoshitsune and company at Hasedō. Upon his defeat to the coalition, he joins them to someday rescue the other hostages at Xuchang. As part of the coalition, he aids Taishi Ci in preventing the serpent forces from attacking Lu Meng at Mt. Tinlao. When the coalition learns from Ayane that Shuten Dōji was at Xuchang, Nagamasa leads the search for the demon and rescues Oichi and Dong Zhuo's other hostages. As he later converses with Deng Ai, Nagamasa becomes concerned for Zhong Hui and helps convince the youth to mend his ways at Luoyang.
During the first half of Ultimate, a doppelgänger of Nagamasa is used by Tamamo to fool Ma Chao into attacking the forces of Wei.
In Warriors Orochi 4, he and his forces are late arrivals of the world, only appearing at Nanzhong, where they are immediately surrounded by Da Ji's demon army. Luckily, he and his wife are rescued by the Coalition forces, who push Da Ji back. Although Da Ji was defeated, Perseus ended up getting captured, and Nagamasa and the rest of the Azai pledge to help the Coalition rescue their ally. A clone of him is later create to defend Olympus from the Coalition.
He later assists the others when it is reported that a woman is surrounded by allies of the Odin's army at Jing Province
During one of the DLC stages, he acts as one of the co-commanders of the Sengoku forces, who fight the members of the Three Kingdoms in a mock battle. While Kiyomori attempts to exploit the situation and attack the triumphant Sengoku generals, Cao Cao and the rest of the Three Kingdoms forces return to lend their support. Together, both armies successfully push Kiyomori back.
And he is reprised by Darrel Guilbeau in the English dub and Hiroshi Kamiya in the Japanese dub.