Yuna and her younger brother, Taka, were born peasants in Yarikawa. Growing up with an alcoholic and physically abusive mother, Yuna became Taka's protector at an early age. A critical point in Yuna's life came when Taka was six: after their mother broke Taka's arm in a rage, Yuna took Taka and ran away. She would learn that her mother was found dead a month later.
Yuna accepted the help of a figure known as Black Wolf, who she believed to be trustworthy. In reality, he was a slave trader and sexual predator of children. Yuna and Taka were drugged, taken advantage of, and later sold to the cruel slavers, the Mamushi brothers. Yuna and Taka, alongside another slave named Ichi, attempted an escape. However, Ichi was recaptured. After their escape, Yuna and Taka presumably live a nomadic life on Tsushima Island until the Mongols invaded. During the events of the game, it is clear that the traumas of enslavement and a difficult childhood continue to haunt Yuna.
Yuna continued saving money wherever she could, in the hopes of moving to the mainland and starting a better life.
After the Battle of Komoda Beach, Yuna finds Jin Sakai gravely wounded. After rescuing him from the beach, Yuna gradually nurses Jin back to health outside of Komoda Town while hiding him from the Mongol army. Once Jin regains his strength, she aides him in recovering his katana, which she traded for food and medicine to care for him. While they hide from Mongol guards, Yuna teaches Jin thief tactics that spark his journey to becoming the Ghost. Together, Yuna and Jin escape Komoda Town. During their escape, Yuna asks Jin to aid her in saving her brother Taka who was taken by the Mongols, explaining that Taka is an expert blacksmith who could make any tool Jin needs. Jin agrees, but stipulates that Yuna must first help him save his uncle, Lord Shimura, from Khotun Khan at Castle Kaneda. Yuna agrees, but requires that Jin gets Yuna and Taka safe passage off Tsushima with Lord Shimura's help. Yuna accompanies Jin in his first attempt to rescue Shimura. Yuna fought alongside Jin to clear the lower castle, but stayed behind to prepare the horses and keep the way out clear. Following Jin's failed attempt, Yuna and Jin reunite in the forest nearby and they part ways, agreeing to regroup at a later time for a larger attack on Castle Kaneda. Yuna begins to gather more information on where Taka is being held.
Later, Jin and Yuna reunite and head to a Mongol prisoner camp where they believe Taka is being held. Unable to risk the possibility of the Mongols executing the prisoners, Yuna convinces Jin to go against his samurai code by striking from the shadows and killing the Mongols in stealth. However, Taka is not there. Yuna and Jin receive information from a Straw Hat that prisoners are being moved to Azamo Bay. Jin meets up with Yuna and her friend Kenji who confirms that Taka is being enslaved as a blacksmith in Azamo Bay. Having tailed a Mongol slaver in charge at Azamo Bay, Yuna, Jin, and Kenji discover that a slaver plans to kill Taka. This is due to a deceptive tip from another desperate and starving blacksmith who claimed his smithing was of a higher quality than Taka's, knowing he could survive if he became the blacksmith they decided to feed. Yuna follows the slaver to Taka, killing her brother's captor and escaping Azamo Bay with him alongside Jin. Shortly after, Yuna and Taka temporarily separate from Jin as they head to Komatsu Forge to work on a grappling hook for Jin that can aid him in his siege on Castle Kaneda. When Jin later joins them in Komatsu Forge, Yuna and Jin drive off the Mongol forces and save fleeing families. After the battle, Taka remarks that he's never seen any samurai fight the way Jin has before. Yuna crafts a tale to explain Jin's superhuman abilities, boasting to onlookers that Jin is not human, but a ghost - a story that sticks and results in Jin becoming known as the legendary Ghost of Tsushima. With her brother safe, Yuna fulfills her end of the bargain and assists Jin in a second siege on Castle Kaneda, resulting in the successful rescue of Lord Shimura and retaking Castle Kaneda from the Mongols.
With her promise fulfilled, Yuna asks that Jin fulfill her request that he and Lord Shimura help her and Taka get off Tsushima, believing there is nothing left for them there. Shimura agrees, but on the condition that she help him and Jin retake Castle Shimura. Yuna is visibly resentful of this condition, but reluctantly agrees. Jin later meets with Taka and Yuna outside of Yarikawa Stronghold, where the Mongols have the Yarikawa townspeople under siege. Wanting to recruit Shimura's old enemies to their fight against the Mongols, Taka, Yuna, and Jin sneak past the blockade through an old passageway the siblings used when they were children. The trio manage to get inside, but fail to persuade the Yaraikawa leader, Ujimasa, to fight with Shimura's army. Ujimasa expresses resentment toward Clans Sakai and Shimura due to their pivotal role in the destruction of Clan Yarikawa many years prior. Ujimasa dismisses Yuna and Jin, saying that he believes the Mongols will move on from Yarikawa, and that the people of Yarikawa can outlast a siege.
Yuna and Jin help to repel the Mongols, hoping that with the help of Clan Sakai, old grudges may be forgiven and the people of Yarikawa will come to Lord Shimura's aid. Yuna and Jin embark on a dangerous mission to find and bring Yarikawa's best archers back to the stronghold. Yuna is increasingly concerned Taka's growing desire to fight the Mongols, believing that he will be hurt or killed, but she reluctantly allows him to come with her and Jin. Later, after successfully bringing back the archers, Yuna and Jin atop the tower in Yarikawa stronghold. To loosen their nerves before the Mongol attack, the two and begin drinking sake together. By nighttime, the drunken Yuna tells jokes about Kenji and opens up to Jin about her abusive mother, who Yuna saved Taka from when she broke her then six year old son's arm in a drunken rage.
After further reminiscing, Yuna and Jin are alerted to the Mongols' arrival and head to the gates. In the ensuing battle, the people of Yarikawa are victorious after Jin kills one of Khotun's best generals, Temuge, and the Mongols are successfully routed. Yuna, Jin and Taka then convince the Yarikawa clan to stand together and aid Shimura in the fight against the Mongols.
Yuna informs Jin about a Mongol warlord, Altan, who has reportedly been terrorizing the people of Otsuna. He has been stealing food and medicine, and if anyone fights back, they are butchered. Yuna and Jin seek the help of her childhood friend, Ichi, who runs an inn that is currently inhabited by Mongol soldiers. Once Jin and Yuna defeat the Mongols, Ichi is angry both that they killed her customers and upon seeing Yuna. Reluctantly, she offers information to Jin stating that even Altan's men do not know where he is located. However, they can bring Altan out of hiding by finding his allies and making an example of them - starting with Japanese slavers, the Mamushi brothers at their farmstead.
Meeting Yuna just outside Mamushi Farmstead, Jin remarks that the place resembles a small fortress. Yuna explains that it is because the Mamushi brothers do not want anyone knowing what goes on behind their walls, because they are slave owners. She reveals to Jin that she and Taka were enslaved by the brothers as children. Recalling some terrible memories of her past, Yuna cannot bring herself to enter the farmstead. Jin offers to go alone, and promises the brothers will pay for the abuse she endured at their hands. They agree that a stealth approach is best, but in order to scare the Mongols with the legend of the Ghost and earn Altan's attention, Jin must not be seen and can only kill the three brothers. After completing the task, Yuna lets Jin know that all of the slaves were provided to the Mamushi brothers by one man: the Black Wolf, who sold Yuna and Taka to the Mamushi slave farm.
After meeting up again outside the Black Wolf's camp, Yuna confesses to Jin that she had a chance to kill The Black Wolf when she was a child, but was not brave or strong enough to go through with it. More Mongols stand in their way but are quickly killed by Jin and Yuna. After clearing the camp, they realize The Black Wolf is on a nearby ship. After killing the Mongol soldiers on the ship, the Black Wolf reveals his presence, leading to a confrontation between him and Yuna. During the argument, The Black Wolf taunts Yuna, saying that Taka was his “favorite”, and that it was she who had brought Taka to him in the first place. Disgusted and disturbed, Yuna kills him. After leaving the ship, Yuna confesses to Jin that Taka, who had fortunately forgot the incident, was raped as a child by the Black Wolf. Yuna blames herself for not preventing the abuse, but is comforted in knowing that the Black Wolf will never hurt another child again.
Jin and Yuna head back to Ichi's Inn and speak with Ichi, finding her wounded. She tells the pair that Altan got their message and said to meet him at a camp near the Kushi-Otsuna border. Ichi is even more bitter now than their first meeting, and expresses a great deal of resentment towards Yuna, who she calls a dishonorable thief with worthless promises. On the way to Altan's camp, Yuna tells Jin what happened between her and Ichi many years ago: Ichi was a slave at Mamushi Farmstead where they met. Ichi looked out for Yuna and Taka, shielding them from the worst punishments. All three had planned the escape, but as they were running, Ichi fell behind and began screaming, but Yuna and Taka kept running, leaving Ichi behind to be re-captured by the Mamushi Brothers. This event left a huge impact on Yuna, who is wracked with guilt and shame.
Altan is a formidable shieldsman, but Jin and Yuna are able to defeat him and his soldiers. Ichi appears claiming that the people are scared of the Ghost, but believes that in the end, Yuna and Jin acted out of necessity.
Eventually, once Lord Shimura has built up enough forces to attack Castle Shimura, he finally gives permission for Yuna and Taka to leave Tsushima and begin their new lives. Informed by Shimura that the Mongols under Straw Hat traitor Ryuzo are preparing to flank their forces from behind, Jin asks Yuna to join him to Fort Koyasan to kill Ryuzo, but she refuses, saying it is not her fight and wants to go to the mainland to live in peace with Taka. Jin reluctantly accepts Yuna's refusal and bids farewell to Yuna and Taka.
Later that night, Taka leaves a note to Yuna, informing her of his desire to help Jin in his fight. The next morning, Yuna finds the note and begins to frantically search for Taka. As she searches for Taka, Yuna runs into Jin. Yuna asks where her brother is, and Jin hesitates. Sensing something is wrong, Yuna runs into the courtyard and to her shock, discovers Taka's beheaded body, the work of Khotun Khan. Grief-stricken, Yuna initially blames Jin for Taka's death, as Taka wanted to be like the Ghost, but the two are alerted by Mongols and Straw Hats closing in on their location and, unwilling to leave Taka's body behind, prepare for battle. They kill the arriving forces in fury and leave the courtyard with Taka's body.
Sometime after, Jin and Yuna honor Taka's legacy with a burial, adorning the pire with his headband. Yuna says to Jin that she now has nothing to live for, as she spent her entire life trying to protect her brother and failed. Having lost her sole life purpose, she decides to stay on Tsushima Island to help Jin fight the Mongols and avenge Taka.
Later, as Shimura prepares to commence the assault on Castle Shimura, Yuna tells Jin that the people of Tsushima are inspired by Jin. Jin admits that he would give his life for Tsushima and for Yuna. During the ensuing battle, Yuna helps Jin take over a hwacha from the Mongols and drives them into the inner keep.
However, the battle ends in disaster, with Shimura foolishly ordering a frontal charge that leaves many samurai dead. Realizing that Shimura's insistence on upholding honor will only bring unnecessary bloodshed, Jin and Yuna execute a plan to sneak inside the castle and poison the Mongols. Yuna gathers up piles of wolfsbane for Jin to use and gives him the Ghost Armor, an outfit that Taka was making for Jin before his death. With Yuna's help, Jin successfully poisons the Mongols and kills Ryuzo in a duel. Jin and Yuna are confronted by Lord Shimura and defend their actions as necessary. Knowing that the Shogun will want someone executed as punishment, Shimura asks Jin to blame Yuna for the dishonorable killings, but Jin refuses to stand down. Before he is arrested, Jin gives his equipment to Yuna, urging her to follow the Khan and continue the fight without him, for Taka.
Yuna eventually manages to track the Khan to the far north of the island. Yuna passes the message to Kenji to inform Jin, who escapes from Shimura's men. Yuna meets Jin, wounded again by local Mongol forces, and helps him escape from their pursuit. After bandaging his wounds, Yuna gives Jin his equipment back and informs Jin that the Khan and his army are gathering in a stronghold on the coast, Port Izumi. They establish a forward base at Jogaku Temple by taking it from the Mongols, then prepare an assault on Port Izumi by gathering their allies and scouting out the Port, deducing that it will be most vulnerable at the next snow storm.
Yuna and Jin meet one last time before the Battle of Port Izumi and reminisce about their journey together, admitting that they cannot live without one another and vow to do all they can to defeat the Mongols, for both of their survival. Yuna and the rest of Jin's allies aid Jin in infiltrating the Port. In a final battle, Jin kills Khotun Khan, avenging Taka, the people of Tsushima, and crippling the Mongol invasion. With the Khan dead, Jin and Yuna leave the port on horseback and decide to focus on routing the remaining Mongols from the island and then start new lives. Yuna is uncertain about what she wants to do, saying that she has nobody left. She tells Jin that as he is the Ghost of Tsushima, he belongs to everyone. Yuna then informs Jin that Shimura sent a letter requesting a final meeting with him, and Jin departs to meet with him.
Jin, branded a traitor by the Shogun and stripped of his lordship, relocates to a dilapidated shack. Yuna finds him there, and the two discuss the next steps for liberating Tsushima. Jin and Yuna part ways to defeat the remaining Mongols.
Hardened by her difficult and traumatic upbringing, Yuna is a shrewd and occasionally ruthless, but ultimately compassionate and loyal woman.
- "The Walls of Yarikawa"
- "The Coward of Yarikawa"
- "The Ghost of Yarikawa"
- "A Reckoning in Blood"
- "Fate of Tsushima"
- "From the Darkness"
- Yuna carries a Tachi with her all the time, though she does not use them in combat until the later part of Act 2.
- Yuna is largely responsible, if not the biggest reason for the legend of the Ghost: she was the one who convinced Jin Sakai to abandon the Samurai's strict code of conduct, and later verbally started the legend in Komatsu to encourage its people.
- In the Japanese dub of the game, Yuna addresses Jin on a first name basis without use of honorifics; considering her status compared to Jin and the amount of time they spent getting familiar with each other, this easily denotes that she's very dismissive or simply oblivious about such courteous customs and formalities.
- Yuna's name means "is dream" or "is beautiful" in the Kanji script.
- "The Black Wolf"
- "The Warrior's Code"
- "The Broken Blacksmith"
- "Hammer and Forge"
- "Shadow of the Samurai"
- "The Walls of Yarikawa"
- "The Coward of Yarikawa"
- "The Ghost of Yarikawa"
- "The Tale of Yuna"
- "Silent Death"
- "Message in Blood"
- "A Reckoning in Blood"
- "The Fate of Tsushima"
- "From the Darkness"
- "Wolves at the Gates"
- "A Gathering Storm"
- "Eternal Blue Sky"
- Ending of "The Tale of Lord Shimura"