Muu Alexius (ムー・アレキウス, Mū.Arekiusu) is a half-blood Fanalis, and the former leader of Reim Empire's Fanalis Corps. He is the owner of the Djinn Barbatos. He is a Dungeon Capturer, having captured one Dungeon and is one of Scheherazade's King Vessels. During the Final Arc, Muu is now a member of Reim Empire's Senate, which is now a Republic, and is also a fellow Ambassador when he attended the assembly of the International Alliance.
Muu is a tall and muscular man. He has long, red hair and red eyes with distinctive markings, due to his Fanalis heritage. Like most Fanalis, Muu has a piercing under his lower lip. He wears a metal cuirass, shoulder plates, a metal skirt, shin guards, sandals, and a large sword that he carries at his waist.
Three years later, Muu's clothing has changed into a simple Roman toga with sandals. He no longer wears any armour like he did before. 
Muu has a kind expression and likes to make other people happy, even people who he doesn't know, but looks up to him. However his attitude can change when danger can come to pass, such as when Scheherazade was seemingly targeted by Magnostadt and he wanted to become her sword and protect the people of the Reim Empire.
When Muu was young, he had met Scheherazade. He heard a lot of the stories from her and Pernadius' adventures. He ended up being by her side when she was changing her bodies.
At one point, he went searching for his brethren, visited Cathargo and met Yunan in the Great Rift. He ignored Yunan's warnings and advanced further in the valley. Although the way there was a tough one and at one point, he even thought he was going to the land of death, his desire to meet other Fanalis won. He had decided that even if he had to die if that was a place where Fanalis should go, he had to find it. As he was on the verge of losing consciousness, he changed into a beast whose body was overflowing with Magoi, intuitively thinking that it was his true form. When he finally saw the Fanalis' homeland, he realised that all of them are beasts. Yunan came and brought him back thanks to his Magic. He said back then that his warning was about not being able to fit in again once the Fanalis knew their true self so they had to bid farewell to all they have on that side and according to him, Muu was still too young.
He also promised Scheherazade to inherit all of her wishes and to not surrender her country to anyone.
Sometime in his life, Muu conquered the 8th Dungeon and obtained his Djinn Barbatos. He also searched for his Fanalis brethren and created the Fanalis Corps with them.
Muu is impressed by Alibaba Saluja after his fight against Garda, and comments on his vitality. Muu asks why Lady Scheherazade came to the Colosseum, as she doesn't like gladiators fighting. She tells him that Alibaba has an air around him and that he piqued her interest. Muu asks if that's what's called the Rukh's guidance. Scheherazade says that Muu comes to the Colosseum a lot, and he says he does this so that it will become even more popular. As he is called Reim's strongest swordsman, when he comes to the matches, the public and other swordsman will be very happy. After an awkward silence, he continues that he wanted an audience with her to talk about something that piqued his interest. He ways that someone wants to interfere with her protection of the Reim Empire's peace: Magnostadt.
He tells her how the capital of Magnostadt is full of Magic Tools right now. He comments on the strangest of how they came to possess such a high quantity of Magic Tools that originally existed only in Labyrinths. He says that he heard that even the lowlifes that frequent Magnostadt's region possess Magic Tools, and that Magnostadt has started to lay their hands on the easternmost province of Reim. Scheherazade apologizes to him that she made him worry and that this story has reached his ears. Muu disagrees and says he just wants her to command him. He says, "Make me into your sword, that would fight the abnormalities of this world and protect the country and people you love." She then pats him on the head and says the face he made was scary and she likes it when he smiles, which causes Muu to blush. Scheherazade tells him that the people of the east are frightened, and are waiting, and that she will protect the Reim Empire. She then adds that in the Kou Empire, there is another great abnormality.
Months later, Muu enters a room with his Fanalis Corps, where Scheherazade, Ignatius Alexius, and Nerva Julius Caluades are talking about going to war with Magnostadt. He tells Scheherazade to leave the defeat of their enemy to them. When Myron Alexius and Lo'lo' get into an argument, he quickly stops them and tells them to get along. He also addresses to all Fanalis, reminding them that they should behave smartly and with a courtesy, to what they agree. Lo'lo' thinks that they have sworn their loyalty to him, not to Scheherazade, and if it weren't for him, they would be just slaves. Muu replies that he searched for them under the name of the Alexius family, on the authority of Scheherazade and the Emperor. He then draws his sword and proclaims, along with the Corps, that they will make their enemy kneel before the Emperor, for the sake of the Reim Empire.
Some time later, Muu and the rest of the Fanalis Corps are on a fleet of boats heading to Magnostadt. When Myron and Lo'lo' get into another argument, he tries to stop it but gets sent flying back. He is then helped up by Alibaba Saluja.
Muu appears along with the rest of the Fanalis Corps when the magicians show their magic of mass destruction. After Myron's intervention, he orders them to hunt down the Magnostadt weapon. Soon after, Muu locates Titus Alexius and tells him to return to Reim. When Titus says that he doesn't want to return because he also has important people to protect, Muu laughs at him and says that he cannot live together with them because he is unnatural, and the same goes for them. He adds that Titus is only a monster who cannot become human because he is a life that should not have been born in the world. Titus is devastated after Muu's speech, but Aladdin comes and comforts him under Fanalis' disgusted looks. Muu asks Aladdin for his reason of coming and hears that Aladdin's intention is to stop them and that sorrowful war.
Magicians surround the Fanalis Corps, but Muu says that they'll never retreat since Magnostadt is useful for Reim Empire, and it would be bad if the Kou Empire got it. They advance and avoid the magicians' attacks until the magicians change the route of the river and the Fanalis are waterlogged. They try to swim to the coast but the magicians electrocute the water with Lightning Magic. Muu and a few other Fanalis like Lo'lo' and Myron Alexius endured the attack while the others got knocked down. Muu orders Yaqut and Razol to take care of others, while he, Lo'lo' and Myron will end the fight in one go because of their small quantity of Magoi. with their Metal Vessel and Household Vessels. They take down a lot of magicians, including Myers, and successfully break the second barrier with just a few Fanalis and their Vessels. Before they do even more damage, the Fanalis are stopped by Aladdin and his 3 Ugo.
Seeing Aladdin's powers, members of Fanalis Corps begin to recognise him as Magi. Muu thinks that it's probably true, because the same thing as with Aladdin happened with that person, making Lo'lo' wonder if he talks about Scheherazade. Muu points his sword at Aladdin, saying that in this case, he can't leave him alone. He concludes that he is not Yunan, whom he met once, and shares his knowledge of the fact that there are supposedly only 3 Magi in the world. He deduces that that Aladdin must be the Magi for Kou Empire and asks if he infiltrated Magnostadt in preparations against the war with Reim. Aladdin replies that he's not Judar or any other Magi, but Muu attacks him. He is blocked by Ugo. Muu then announces that he will remove all obstacles against Reim. He then questions Aladdin what is the different between a Magi and the other magicians if all he does is fight like Matal Mogamett.
Muu laughs off Aladdin when he says that he will end the war without killing anyone, thinking that stopping the war alone is impossible, not to mention without any victims. When Aladdin begins to show his powerful Magic, Muu encourages his troops that even he is a human and isn't unstoppable. He exclaims that there's a little more left before they reach the enemy's headquarters, making his soldiers more determined. He then orders his army to follow him and advance, guiding them. However, Aladdin uses sand to push all soldiers behind the barrier, which was restored in the meantime, what destroys Reim's troops fighting spirit. Furthermore, Aladdin orders them to leave and go back to their country. Muu prepares his Metal Vessel, while seriously looking at the Magi.
Muu invokes Barbatos, and changes to his Djinn Equip form. From the shore, he shoots an attack that destroys everything it touches. Myron explains that it wasn't provided to enter in his Djinn Equip until the Magnostadt conquest was almost done, but Muu considered that the real threat was Aladdin and not Mogamett. He approaches Aladdin destroying several rocks and destroys Aladdin's Borg and his wand. When he tries to kill Aladdin, his Djinn Equip starts to vanish, but he makes his last effort and summons his Extreme Magic. However, before he could execute it, Alibaba appears and blocks him. He comments that he never thought Alibaba would be the one to stop him, and deduces that he didn't come as an ally with that kind of appearance. He then turns back.
Muu is exhausted and falls down, so Myron, Lo'lo', and other members of Fanalis Corps join him. Muu says that he didn't imagine that Alibaba would be a Dungeon Capturer but listens to his explanations. He is surprised when he sees that Scheherazade has appeared, and with difficulties he bows. The Great Priestess says to Muu to retreat the soldiers temporarily, and he, disgusted, asks why. He seems shocked when Scheherazade replies that Aladdin is probably gazing at the same scene as Yunan. He waits with the Reim army while the Great Priestess, Titus, Aladdin and Alibaba have their talk.
Some time later, Scheherazade decides to use the last shard of her power and defeat as much Mogamett's Black Djinn as she can. Muu appears along with the rest of Fanalis Corps to aid her. Myron comes to him and Lo'lo', worried about their condition. She tells them in tears that they shouldn't act recklessly again, to which Lo'lo' answers that they're fine. Then, both of them pat Myron's head.
During the fight, Muu commands soldiers to not let their enemy enter Scheherazade's barrier which protects the whole Reim's fleet until the fleet has gone. He orders them to protect it to the end.
He then appears during the fight against the Medium and breaks its Defensive Wall. He addresses to Scheherazade, saying that thanks to her Transfer Magic Square, they completed the retreat of the wounded soldiers and summoned reinforcements from the Reim Empire, including their Metal Vessel users. Alongside Alibaba, the Seven Seas Alliance's members and Kou's warriors, he performs his Extreme Magic to deliver the finishing blow to the Medium.
The enemy starts falling into pieces. Muu's Djinn Equip wears off and he joins one of Reim's balloons, saying that he attacked it with his full power. However, they are still not able to defeat it completely, as it regenerates. After reaching the grounds, Muu forcefully hits it with his fist and curses. He shouts asking if even Scheherazade's last Magoi wasn't enough against it. Asked by Aladdin what he meant, he explains that they were able to use their Extreme Magic one more time thanks to her and because of that, she is now among the dead. Upon hearing it, Aladdin asks what about Titus and Muu, with pained expressions, says that Titus died a while back.
After the fight is over, Muu listens to the conversation between Sinbad and Kouen Ren. When Sinbad mentions that the Seven Seas Alliance and the Reim Empire have formed an official confederation, Muu confirms that he's speaking the truth. He says that Scheherazade has made that decision just before going into her last battle. When Sinbad declares that he wants to use all the power he has to return Magnostadt to its former glory, Muu wonders if he continued to send all those letters to Scheherazade because he was expecting that such a moment would come and curses him. He seems a bit surprised when Kouen wants to take Aladdin with him. After that, Alibaba introduces him to Morgiana and he stretches out his hand to her.
Afterwards, he is notified by his subordinates that the Transfer Magic Circle has sent them something from their motherland. He reminds his soldier that he entrusted them with Magnostadt's related issues and tells him to calm down and tell him what was sent. Much to his shock, Titus is brought before his eyes. When Titus is joined by Aladdin, Sphintus Carmen and Marga, he watches other soldiers that go back on their huge birds.
As they are walking alone, Morgiana asks him if she should keep silent about meeting him there, to which Muu comments that she's smart and kind. He reveals to her that he came to meet with Kouen and Sinbad will probably hear about it. He adds that he is fine with it and asked why he points out that Reim is now in a difficult position with Scheherazade dead. He says he doesn't want both Kou and Sindria stealing its power in front of his eyes. Morgiana notes that they are allies, but Muu explains that they pose no threat to Sindria and Kou and are no more than a third power. Once the Reim Empire relies on either of them, the biggest war will begin. Morgiana comments it with "That can't be...!!".
Muu says that he was hesitant to tell her the truth about the Great Rift before it happens. In Magnostadt, Morgiana told him what she has done to meet her brethren and Muu reveals to her that he himself had tried journeying to the other side of the Great Rift when he was around her age, much to her shock. He ignored Yunan's warning and saw the scenery that lies behind the valley. Morgiana asks him why he kept quiet about it in Magnostadt. He replies that he is still unsure if he should tell her, but she has the right to know and to decide her future after the summit. In his story, Muu's journey was much like Morgiana's, but as he was reaching his destination, he felt that he was becoming a beast and realised that the Fanalis on the other side were not humans but beasts. He was teleported back by Yunan before crossing fully to the other side.
After hearing it all, Morgiana thinks that it's alright and as long as she won't cross the valley, she will be able to live together with them. She asks Muu what will he do, but he replies that nothing, believing that he has duties left unaccomplished. He recalls his past with Scheherazade and concludes that now that she died, he will protect the Reim Empire. Morgiana inquires how many of his men abandoned everything and went to their homeland after hearing his story. Muu answers that none and Morgiana says that it's the same for her; there are two great heroes for her on this side. With a smile, Muu tells her that he knew she would say that and tells her to be wary of Sinbad.
At the summit, Sinbad brings with him the Yambala Gladiators in order to threaten the Kou Empire. Just then, Muu and the Fanalis Corps appear on the side of the Kou Empire. Sinbad tries reminds Muu that the Reim Empire entered into a confederation with the Seven Seas Alliance. Muu says he is very good "friends" with Kouen and he met with him personally before the summit. Sinbad offers to go drinking with Muu after the summit so that they could become friends also. Muu says he doesn't drink so they won't be able to enjoy the alcohol together. Yunan appears and introduces Aladdin and Titus. Aladdin tells everyone that he wants to tell them something no one else in the world knows about, Alma Torran.
As Muu is a half-blood Fanalis, he's not as strong as the Pure Blood, so he is comparatively weaker than the average Fanalis but still has great physical strength. Muu was also born with exceptional speed. Muu, as a Fanalis, maybe has superior hearing and smelling.
Besides his physical prowess, Muu has some skills with a sword, as he is known to be the strongest swordsman of the Reim Empire.
Barbatos is the Strength Djinn that Muu obtained when he conquered the 8th Dungeon. He is the Djinn of Hunting and Nobility. Muu's Metal Vessel is the sword that he always carries at his side. By activating his Metal Vessel, he can increase his slicing power to create aerial slashes. Muu's Household is made up of his sister, Myron, and his subordinate, Lo'lo', and possibly other members of the Fanalis Corps.
|“||Spirit of Hunting and Nobility. I command thee...Be clad in my body. Dwell in my body. Change my body into a great Djinn, Barbatos!!!||”|
—Muu, summoning the powers of Barbatos
- Djinn Weapon Equip: He compresses Barbatos' Strength Magic around his weapon changing it into a javelin. This javelin is capable of easily breaking through rocks and barriers in an instant with only a thrust.
- Djinn Equip: Muu's Djinn Equip appearance is that of a lion. His hair becomes a long silver mane, with two metal hair clips holding two bangs at the front, and his eyes turn from red to turquoise. His skin gets darker and he has pointed ears. Muu gains feline-like feet covered in a silver armour over the lower half of his body, with white wings at his ankle. He also gets a pair of wristbands connected to a pair of armbands by chains. In this form, similar to a cheetah before running, his feline legs act like a spring to increase his speed and power making him capable of crossing massive distances in an instant. They compare this to his body becoming a sword capable of breaking through anything. It's been stated that he has a low quantity of Magoi since he's a Fanalis, and his Djinn Equip lasts no more than one minute.
- Bard Romh (Barbatos' Javelin): It is able to produce shock waves using Strength Magic that are able to fly to far distances. These shock waves can come in the form of whatever attack is used for (eg. if a punch is used, the shock waves would look like a bullet, but if a sword was used it would be like a slash of compressed air sailing towards the target). Each shock wave is easily capable of breaking a Borg of a Magician and severely damaging them.
- Bard Longineus: Muu's Extreme Magic takes the form of a huge sword made of blue light. Considering that Muu was far from Magnostadt when he tried to use this spell, it can be assumed that it was capable of destroying the city even from a long range. However, the full effects were not seen, since the spell was stopped by Alibaba.
Muu is one of Scheherazade's King Vessels and is on friendly terms with her. He wishes to protect Scheherazade and everything she loves, the Reim Empire and its people. That loyalty is what may have prompted Titus to call him "Lady Scheherazade's First Subordinate".
He is a descendant of her First King and has known her since he was a child. Muu has always considered her his hero and never thought that her act of changing bodies was ugly, but instead admired her motherly love for her country. He desired to inherit her wishes and promised to protect Reim after her death.  He has a crush on her. 
Muu took an interest in Alibaba when he witnessed him back in the Colosseum. He has also battle Alibaba in the Colosseum a few times and Alibaba has even draw blood from him. He also let Alibaba come with them when they were heading to Magnostadt.
Lolo respects Muu a lot, and look up to him as well.
- Muu has the same last name as Titus Alexius (a subordinate of the Reim Empire's Magi, Scheherazade), Myron Alexius (his sister), and Ignatius Alexius.
- According to Ohtaka, Muu's loyalty to Scheherazade comes from the fact that he was born as a descendant of her first King, Pernadius, so it was his fate all along.
- He likes to participate in tournaments on his days off.
- His speciality is sword fights and his hobby is sword dancing.
- He is weak to protracted wars.
- His favorite food is meat and he dislikes sweets.
- He is fond of older women, while he dislikes people like Yunan.
- He is worried about the Fanalis.
- He tells Sinbad that he doesn't drink, which is a lie according to Myron, who said he could drink like a fish.