Yuuya Mirokuji (弥勒寺優夜 Mirokuji Yūya) is the last boss from Exclusive Underground -Dark Night- (閉鎖区 Underground -Dark Night-/Heisaku Underground -Dark Night-), and the ex-captain of a military outpost of Team STRAY dogs. He used to be the best friend of Shou, the hero of the story, but he murdered their friend Rokkaku Araki and Shou's sister, Kokonoka, and deserted the team. He established the association Arajin and conquered Sacred Tree Kuronagimaru and the spirit Hangaku. In order to gain control of the territory of Adachi ward, which had turned into a lawful land after a huge natural disaster, he fights against Shou.
Yuya is a violent and aggressive person who enjoys picking fights, though he is shown to have a sense of honor. He is not interested in making his creator alter his world, being fine with the way he is. When confronting Mamika Kirameki he states that he hates dealing with girls who think that they can get away with things by crying. Yuya is also kind of cocky warning Mamika that he is strong and in his world apparently he is the final boss.
Yuya questions Mamika if she is an ally of Altair and begins to take a step towards her only to be attacked by Aliceteria February, after blocking Alicetelia's lance, Yuya states that the two of them fighting is fun. Alicetelia is then forced to flee with Mamika. After the fight was over Sōta Mizushino was told to stay back by Selesia as him and Takashi Matsubara make their way towards Yuya, but Yuya replied by stating that they appear to not like him even though he saved them, and helps up Selesia who fell over after taking too much damage from the fight with Mamika, and suggests that they get out of there as they begin to attract a crowd.
Selesia Yupitiria and Yuya talk at a diner with Meteora Österreich, Sōta and Takashi. Yuya mentions that he hasn't eaten anything since arriving in the human world, but notes that he uses the same currency in the human world as in his world. When Meteora asks him how much he knows about what is going on, Yuya states that they live in worlds created by other people and adds that it cracks him up. Yuya then went on to mention someone named Syo who is one of his friends back in his world. When Selesia asked Yuya if he knew Military Uniform Princess, Yuya replied that he doesn't remember and is not interested. Meteora offered to bargain with Yuya, in exchange for information from Yuya, Meteora will buy him a meal.
Yuya tells them that he meet Altair soon after he was transported to the human world a while ago. Yuya states that Military Uniform Princess was a snob, because she looked like a kid, but the way she talks makes her sound better than the person she is talking to, and that she was with an old guy who really made him mad, and then they got into a fight, and he has not seen her since.
Yuya mentions that Altair has told him his plans, but he is not interested, because it is like being kept in a cage, and there was no point in fixing someone else's cage, because likes living in the cage in a way. He says he wishes his friends were there with him, including Syo. When Meteora asks if he is interested in meeting his creator, Yuya said that he has a few things he wants to say for making their messed up worlds and got in the way of their relationships, but Yuya does not care about his creator, because to him the creators are just normal people and not gods like they imagined.
Yuya just wants to meet his creator to ask a few questions and asked Meteora and Selesia if they want to meet their creators as well. Selesia then replied that she has already meet her creator and directs Yuya to Takashi, who said that he is her author, which got Yuya interested, and asked them if they have tried revising Selesia's character description, and was disappointed to find out that they haven't even done it yet. Yuya then asks Takashi for a cigarette and begins to smoke noting that it tastes better than the ones from his world.
When Meteora asks why Yuya though about having the creator change their world, Yuya responds by stating that the creator can also change the abilities of the character that he or she has created. Yuya then asked why were they chosen to leave their worlds for the human world, and states his theory that they were selected, because they have left a lasting impression on many people back in their own world, and that the ones who stood out were able to come to the human world.
Yuya then puts out his cigarette , gets up thanking them for the meal and stating that he understands the things he did not before. When Selesia tries to stop him, Yuya responds that he can do whatever he wants, because that was how his character was created. As Yuya walks out he states that he wants to have fun, that he won't cause them any trouble and that he is the type of person that never forgets what others have done for him, and he said "Bye," before leaving.
In episode 7 Yuya confronts Blitz Tokar and apologizes for leaving in the middle of their fight. Yuya continues adding that he hates being indebted to other people. As Blitz takes aim, Yuya summons his companion Hangaku who blocks Blitz's bullets and chases after Blitz, but then goes after Alicetelia February, who blocks the attack with her lance. Yuya ambushes Blitz, but his attack is blocked by Mamika, who forces Yuya back.
Yuya fights Blitz and Mamika, while Hangaku battles Alicetelia. Yuya appeared to have been too much for the three of them, but then Selesia gets in the way between him and Mamika asking him if he like hurting children, to which he responds if that is how she is going to repay him for helping her out. Yuya said that he was only interested in fighting Blitz if Mamika had not gotten in his way.
Rui then arrives in his mech forcing Blitz, Alicetelia and Mamika to retreat. Rui and Yuya are seen later eating on sofas while watching television, and said that he is not under custody, since he came on his own will, because if he stays with them then he might have a chance to fight Blitz again.
Meteora offers to watch over him with Selesia, but Yuya says that he won't go out of control and gives Meteora the nickname "Metchin," which Meteora does not like. Yuya was then annoyed when Rui changed the channel, as he took back the remote and changed it back. When they talked about Magane Chikujoin, Yuya asked if hunting her down is the next game. Yuya then states that both him and Rui have changed, because their character descriptions have been hidden in the plot, and the only way they are revealed is when the character loses their purpose and constraint, and assumes that Magane has changed as well. Yuya then attends a meeting with everyone else.
Yuya was finally able to meet his creator Yatouji Ryou, and summons Hangaku to lift Yatouji by the shirt.
Yuya and Meteora then saves Sōta from Magane before Alicetelia arrives to fight Meteora. During the fight with Magane, she was able to take Hangaku away from Yuya. Yuya later challenges Blitz to a rematch as he and Altair arrive. As Blitz corners Yuya, the two of them were able to see Selesia's transformation.
Powers and Abilities
Yuya is very proficient in his swordsmanship as he's able to block bullets shot from Blitz Tokar's handgun. Yuya can also release powerful blasts of wind from his blade when slashing or even just hitting the ground with the pommel of his blade. However, in terms of pure swordsmanship, Alicetaria February notes that Yuya fights like someone "who doesn't even know the basics of how to fight."
Kuronagimaru - Yuya wields a full black wooden sword with one red line going straight down the middle of the blade. The blade is strong shown to be unscathed when Yuya used it to block Mamika Kirameki's Magical Splash Flare supposedly her ultimate spell.
CompanionYuya can summon his own companion he calls Hangaku. He has admitted to Mamika Kirameki while in battle "I don't like to use this against girls" with next saying "but I'm not the type of guy that would stop himself from using this to smash in your brain" implying that it has a considerable amount of strength. His companion seems to take on the form of a woman with a purple-reddish robe and a huge naginata for battle as well as a mask that covers her eyes.
Yuya has gained the ability to create ice from his blade.
- It can be assumed, that Hangaku is based on the female warrior samurai Lady Hangaku (坂額御前 Hangaku Gozen).
- Yuuya Mirakuji's summoned partner has been likened to either a Stand, a Persona, or likely the case due to what is said about him, a Susano'o, like Sasuke Uchiha's. The Big Bad has never been also The Rival in Persona, and in Jojo, not with a friendly rivalry or a classic "Punch Ghost" Stand. It could be also a reference to the shamans from Shaman King, particularly the character of Ryu (a thug with a wooden sword, just like Yuuya). His fashion sense somewhat resembles visual kei and with it, Iori Yagami.