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Yuni, also called Uni in Reborn! Colore, is the daughter of Aria and the granddaughter of Luce. She is a young girl who is the Millefiore Famiglia's former second-in-command and the current Boss of the Giglio Nero Famiglia as a result of the early death of her mother, whom she did not know was a Mafia Boss. Yuni is the 3rd Sky Arcobaleno; thus, she is afflicted with the Sky Arcobaleno curse, which curses the Sky Arcobaleno to a short lifespan.
Yuni wears the Giglio Nero clothing that her predecessors wore: a big, white, mushroom-shaped hat with half of the emblem of the Giglio Nero on it and a large black bar at the sides, with two orange stripes flanking it. Her Giglio Nero clothing also consists of a long coat with the Giglio Nero emblem at the bottom right and left sides. Underneath, she wears a pant-skirt and a short blouse that reveals her stomach. When in her Millefiore uniform, Yuni dons a black jacket to symbolize that she is part of the Black Spell. However, she also wears a White Spell Millefiore coat over it. After the Future Arc, when Yuni returns, she wears a white uniform that is similar to the Millefiore one.
She has blue eyes and her hair is short in front, but longer at the back. In the manga color spreads, Yuni's hair is a medium to dark blue like her eyes; however, her anime appearance dons a darker hair color of dark teal in nature.
Yuni is a kind-hearted and polite girl, thanking people multiple times for helping her. Yuni is also unselfish, willing to sacrifice her own life in the future to revive the dead Arcobaleno to restore balance to the Tri-ni-set. She's also accepting and forgiving, harboring no ill will towards Byakuran despite everything his future self had done in the future.
Yuni inherited the Sky Arcobaleno Pacifier from her mother, and this Pacifier has been passed down in their Famiglia for three generations. When Aria passed away, Yuni learns of the Mafia, and the leadership role she must play for the Giglio Nero Famiglia. Yuni was originally kind-hearted and caring towards others, and during that time, she came to know Reborn, whom she knows as her uncle. The Giglio Nero Famiglia was losing strength and power. In order to keep the Famiglia's power and avoid any of her Famiglia members hurt even further, she meets Byakuran, who schedules a meeting with her. After the meeting, Yuni emerges from Byakuran's office with a completely different attitude and personality (according to Shoichi, her heart was dulled with a powerful drug). She then announces that the two Famiglias will merge and become the Millefiore Famiglia, in which Byakuran would be the head. As a result of the merge, she has become bitter and cold-hearted.
She was the head of the Black Spell and Captain of the 1st Calendula Squad. After the first round of Choice, she had recovered from the drug and intervened to say that the promise that Shoichi said that they made is valid, and Byakuran should honor it. When Byakuran ignored her suggestion, she decided to leave the Millefiore Famiglia and asked Tsuna to protect her.
In the Future, she ranks as the Millefiore Famiglia's overall second-in-command and the leader of the Black Spell Division.
After the Choice battle in which Vongola team lost, Shoichi demands a rematch based on the fact that Shoichi won the last game of Choice that he played in university after which Byakuran said that Shoichi was allowed to make any condition in their next match. Byakuran refused, claiming not to remember the conversation. Yuni then shows up claiming that as co-head of the Millefiore Famiglia, she should have a vote in the matter. She reveals that she is no longer under the influence of the drugs that Byakuran had given and that she had protected her heart "by going to a faraway place". When Byakuran refuses her request she breaks of the pact between the Giglio Nero and the Gesso Famiglias. She then asks Tsuna to protect her while showing him that she has taken back the Arcobaleno Pacifiers.
When Byakuran tries telling her to return them she states that what Byakuran has cannot be called Tri-Ni-Set because if the hearts of the owners are dark the Pacifiers will not show their true shine. She then proceeds to restore them with her power, which triggers Byakuran anger and greed, prompting him to attack her and to force her back only to be stopped by Reborn's bullet who states that no matter the circumstances he cannot allow him to harm the leader of the Arcobaleno who he also states is the granddaughter of an acquaintance of his.
A few moments later, Byakuran proposes to Yuni that the Vongola Rings stay with the Vongola Famiglia in exchange for her return to the Millefiore side together with the Arcobaleno Pacifiers. But Yuni refuses the proposal saying that she knows why Byakuran wants her back. She also adds that Byakuran does not have any right to the Tri-Ni-Set since the Vongola Rings and Arcobaleno Pacifiers are properties of the Vongola and Arcobaleno respectively. She swears that as long as her soul exists, as the Sky Arcobaleno that carries the parts of the Tri-Ni-Set, she will not allow any scramble for the Tri-Ni-Set. Moreover, she invalidates the Choice Game.
In response, Byakuran threatens Yuni that harm will befall the members of the Black Spell if she continues with the betrayal. But Yuni stays firm with her decision and once Tsuna got resolved with helping her, she proceeds to escape back to Namimori with the Vongola Famiglia.
After she visited Lal Mirch in her hospital room and asked her to take care all of Arcobaleno Pacifiers, she along with Tsuna and the others return to the Past and summon Vongola Primo through Tsuna's Vongola Ring. Her real identity was kept as secret so it won't change the Future. Vongola Primo appears, answering Yuni's will and accepting her condition which is still unknown what kind of condition she given to him so he can help Tsuna. She then staying at Tsuna's house for a while and become his tutor after receiving the Sky Pacifier from Aria in the past. When Reborn told her that she might meet her in this time, she refused saying it’s okay and that this is not the time they should meet and Aria knows of this.
Later, without Tsuna's knowledge, she transferred to Namimori Junior High School, as she was his tutor. She was seen at all succession tests but didn't do anything but watch. That is, until Daemon Spade's succession test. Yuni, along with the other girls were trapped inside a field in Kokuyo Land by Daemon as hostages. As it gets more and more difficult to breathe, Yuni uses her power to ease the breathing. After a while she gets exhausted, but was able to guide Reborn and the other Arcobaleno to her location. She watches both Tsuna and Chrome get their inheritance. As she prepares to leave, she thanks Tsuna's mother and the rest for their hospitality and goes back to the future with the rest to face Byakuran and the Six Funeral Wreaths.
At Kawahira's residence, Yuni was kidnapped by Torikabuto who was disguised as Lambo but later was defeated by Tsuna with the help of Chrome's Vongola Box Weapon. Yuni is later seen at the final showdown between Millefiore and Vongola. Yuni was summoned by the resonance of 2 strong Sky Flames into the battlefield where Byakuran and Tsuna were fighting. Yuni later sacrificed herself to revive the dead Arcobaleno by using her Flames, but it grew weaker because she feared death. Gamma later got inside the barrier due to Basil's Box Weapon and coax Yuni not to be frightened of death since Gamma will accompany her together. Yuni and Gamma then became the sacrifice to revive the Arcobaleno.
Yuni, before dying, told a few people from the past about Tsuna and the Guardians' battles in the Future using the Flame of Life.
Future Yuni emerges from the forest as the Sky Arcobaleno pacifier becomes inflamed, showing that the successor had arrived. She had chosen Byakuran, the Six Funeral Wreaths, Gamma, Nosaru, and Tazaru to be her representatives for the Representative Battle of the Rainbow. Later, Yuni is seen telling Byakuran and Gamma that they had some planning to do after Tsunomichi explains the rules of the upcoming battle. When Byakuran arrives in Japan and offers to Tsuna that they form an alliance, the former reveals that Yuni was on some "business" before the battle.
Later, Yuni appears with Reborn and the others. Reborn asks Yuni if Byakuran and the others were all right, to which she responded that Shoichi and Daisy were tending to their wounds with their Sun Flame's Activation characteristic. Reborn asks Yuni if she foretold the current situation, the latter replying in the positive. Yuni explains that she had known about Bermuda and his anger towards the Arcobaleno, but didn't understand what the anger signified. Colonnello asks Yuni if she could tell any more of the future, but Yuni responds that she only saw Checker Face's face, and that each time she saw it, her heart hurt as if it was being gouged out. Reborn, however, hands Yuni a handkerchief and tells her not to worry too much, stating that he didn't like seeing her like that. Yuni tearfully thanks Reborn.
After the third day of battle, the Arcobaleno (sans Skull ) meet with Reborn. When Reborn gets into an argument with Colonnello, Verde, and Mammon, Mammon accidentally hits Yuni with an illusionary attack. This ended the fight, as the Arcobaleno parted ways immediately afterwards.
Aria is Yuni's mother and their relationship status is quite vague; however, Yuni has been shown to love her mother very much, willing to take leadership role as Boss of Giglio Nero Famiglia in her place. Aria also cared for Yuni, as she gave her position as the Sky Arcobaleno to her so Yuni could have a chance to be freed from the curse that shortened her lifespan by taking part in the Representative Battle of the Rainbow.
At first, Gamma was in disbelief that Yuni was Aria's daughter; therefore, he grabbed her and wanted to kick her out of their base. However, at their first meeting, when Gamma saw that one of her sleeves was wet, he realized that she had been crying and had hidden her tears by wiping them on the sleeve, which is similar to what Aria had done shortly before her death. After that, Gamma quickly saw the similarities between Aria and Yuni and was then completely protective and loyal to her, calling her "princess." Yuni and Gamma share a close bond that is perhaps more than normal boss-subordinate relationship. Reborn had also stated that Yuni is fond of Gamma, and Yuni herself said that she loved him as Aria did. She has also stated that, to her, Gamma is like the mother that she had lost. Gamma also cares deeply for her and has been shown to be unable to decline Yuni's requests, like when Yuni decided that Byakuran and the Real Six Funeral Wreaths would be her representatives along with him, Nosaru, and Tazaru, and also when she agreed to form an alliance with Tsuna.
When Yuni asked Tsuna to protect her, he, at first, panicked and hesitated to accept her request. But eventually he, and the others, agreed to protect her. She became his mentor during the Inheritance Succession Arc and he protected her throughout the duration of the Future Arc. When she died, he was angered greatly and stated that Byakuran was unforgivable for killing Yuni.
Byakuran was the one who sealed Yuni's soul in order to get all the Arcobaleno Pacifiers and the two famiglias to combine into the Millefiore. He used Yuni, referring her as his toy, and was angered when she died in the Future because she was the link to the Pacifiers. Even though he treated her wrongly, she still asked the younger Byakuran, and his Funeral Wreaths in the present time, to be her representatives in the Arcobaleno battles along with Gamma. She harbor no hard feelings to him for what he did do in that Future and they appears to be on better terms than they were in the future, to the point where Yuni trusts Byakuran's judgement to form an alliance with Tsuna in the Representative Battle of the Arcobaleno and genuinely concern from the bottom of her heart of his well-being. The present Byakuran also returns her feelings the same, revealing that her kindness is what connected him back into reality and expresses his desire to protect her, showing that he cares for her.
Yuni has the power to read people's mind and feelings; it has also been said that she knew what would happen to herself before she met with Byakuran. This Ability seems to have expanded to the Ability to see the Future, although that Ability has been growing weaker due to the curse she's bearing. She reveals that, like Byakuran, she also possesses the Ability to share her mind with the alternate versions of herself from different parallel worlds. She, like the other Sky Arcobalenos, Aria and Luce, has the power to revive or reconstruct her fellow Arcobaleno who have died temporarily at cost of her own life. It also appears as though she was the one who willed the Vongola Rings to bring back Vongola Primo during the Inheritance Succession Arc. Additionally, the Tri-Ni-Set seems to respond to Yuni's wishes, most likely because she is the boss of the Arcobaleno. Byakuran stated that the Sky Arcobaleno has authority over the Tri-Ni-Set. During the Inheritance Ceremony Arc, Timoteo reveals that he knows everything that happened in the future that Yuni sent him through his dreams.
- Yuni, in the future, held all the Arcobaleno Pacifiers except for Colonnello's, which was possessed by Lal Mirch.
- Like her mother and grandmother, she has the emblem of the Giglio Nero tattooed under her left eye. Her ancestor has the same tattoo but under the right eye instead of the left.
- She has a character song called Kokoro no Hoshi.
- The character bio for Yuni on the official Reborn anime website mentions that Yuni appears to be about 10 years old; however, her age has not been dead set.
- Future Arc Yuni is of her Future self from the present. Since Tsuna and company was sent not quite ten years into the Future, Yuni couldn't be older than ten, making Shoichi's warning of present and future selves being in the same timeline not an issue when she travels with Tsuna and company to the present during Inheritance Succession Arc. Curse of the Rainbow Arc Yuni looks slightly younger than her former Future Arc self, hinting that her age has to do with Aria's disappearance or her Future self returned.
- Akane Tsunemori from Psycho-Pass bears a physical resemblance to Yuni, as both characters were designed by Akira Amano.