Muru Muru (also known as "Mur Mur") is the servant of Deus Ex Machina and serves as a judge along with him in the Survival Game. She rarely appears in the main storyline (until the last few episodes), usually serving as comic relief in side-stories in both manga and anime. As the series progresses she reveals herself as the main antagonist who plots behind Deus' back to manipulate the events of the game for her own personal amusement. She also appears as a main antagonist in Future Diary: Paradox.
Correlating with her appearance, Muru Muru is a childish individual who seeks nothing more than to have fun with the survival game. She also is quite mischievous and more than in one occasion has been seen disguising herself as other people (and is actually mistaken to be the real one, despite her complete lack of a true disguise), to sneak in places for seemingly no reason at all. She's also known to be an avid manga reader and it is suggested she reads mostly shoujo manga.
Despite these peculiar quirks, (the first) Muru Muru has shown to be in fact a manipulative, cunning, and sneaky individual who plots behind Deus' back and uses the other participants in the way she sees fit to make the game more fun for her, thus indicating she has little if any loyalty towards Deus, although she does respect the game rules and does not use Deus' powers for herself.
She also seems to belittle humans, or at the very least non-participants, believing the likes of Aru Akise to be unfit to enter the Cathedral of Causality, seemingly being homophobic towards him, although it might because he is really Deus' Observer in the game. The two share an antagonistic relationship towards one another throughout Future Diary: Paradox.
In contrast, in the third world, Muru Muru seemed to openly welcome Akise and told him to continue his hard work, indicating that this only applies to the Muru Muru of the first world.
Being Deus' servant, Muru Muru has several superhuman abilities of her own. She can teleport herself from the Cathedral of Causality to the real world as she pleases, can teleport with enough speed to evade an attack from Deus as well as teleport others. She can also travel through time, and even show events of another timeline in a cinematic fashion.
She's also a capable fighter, being able to manipulate a large orb to easily smash debris or even trap people in an illusion-world, as well as stop a bullet with her bare hands. In the anime, Muru Muru shows several extra powers including summoning black-coloured projectiles which can take the form of different objects, can manipulate shadows, fire an energy blast from the trumpet she carries on her person, and can form explosives that are stronger than those of Minene Uryu. She is also capable of manipulating memories, either removing or implanting them at will, the latter being apparently a much longer process. Despite all of this, it is seen that her normal child-form is in fact restrained, and when the seal placed on her is broken, she becomes a bigger monstrous version of herself who is much more destructive. While it is only glimpsed in the manga, Muru Muru's true form in the anime turned her skin a murky grey, and gives her red eyes and fangs. In this form, she can attack at near supersonic speeds and fights with rabid, animistic strikes that prove enough to beat down Minene when she has a portion of Deus' powers.
It is suggested that she has powers that rival or are close to Deus himself, as even when Deus does know that she's plotting against him, does not act directly against her, although this could be because of his decaying lifespan, and resorts to mostly restraining her rather than destroy her.
Although Muru Muru is loyal to the god she is currently serving, she has no qualms about manipulating other gods for her own god's benefit. One such example of this is when the first Muru Muru tricked the second Deus and altered the course of the survival game for her own amusement. In the post-credits scene of Episode 19, however, she is seen at Mother's Orphanage with Orin Miyashiro, who asks her about her parents. Muru Muru is then shown to think of Deus at this and the two continue discussing Muru Muru's "parent", with very different images in mind.
The First World
Muru Muru assisted Deus in the first survival game, a pair of sealing braces put on her wrists to prevent her from using the full extent of her powers. However, Muru Muru became enthralled with the fun she could get out of the survival game and eventually sided with Yuno Gasai when she became God after Deus' death. Yuno and Yukiteru Amano had attempted a double suicide together, unwilling to live without each other. However, Yuno faked her death and became God in order to resurrect Yuki, only to discover that resurrecting the dead was impossible, even for a god. Muru Muru suggested that Yuno change this, giving Yuno the idea to perform a time leap to the past to be with Yuki. However, upon doing this, Yuno and Muru Muru discovered they had ended up in a parallel world, one year into the past, where a second Yuno existed.
The first world was implied to have been obliterated.
The Second Survival Game
Unwilling to let someone else be with Yuki, even her own other self, Yuno ventured into her second self's house and slaughtered her with an axe. While Yuno is clearly shaken by murdering her other self, Muru Muru enters with the second Yuno's phone, giving to the first in preparation for the second survival game. Muru Muru tries to encourage Yuno to become God once again, but Yuno admits she does not care about becoming God, only wanting to be with Yuki. Muru Muru asks her what will she do when only she and Yuki are left alive, Yuno giving her a cryptic smile.
At some point, Muru Muru encounters her own second self and imprisons her within Yuno's illusion space to replace her, unnoticed by Deus. Both Deus and Muru Muru pose as Yuki's imaginary friends until the start of the second survival game.
The second Muru Muru, during the end of the final battle, escapes her prison when Yukiteru breaks free from his illusion world, shattering the container (a massive ball) in the process. She reveals herself and intercepts a bullet sent by Keigo Kurusu at Yukiteru and Yuno as they embrace. She then restrains the first Muru Muru via way of several black hands. After Yuno stabs herself, Muru Muru grabs Yukiteru and abruptly carries them off to the second world, his and her proper world.
For ten thousand years, she was stuck in a limbo, reading a rotting manga book as Yukiteru, now the god of time and space, refused to create anything and just sat, mourning Yuno. The Yuno of the third world suddenly broke through the barrier between worlds and, now with the first Yuno's memory, became a goddess as Deus allowed her to. She was implied to have lived through four more timelines, gaining four more versions of herself in the process, adding to a total of seven.
The Third World
The first Muru Muru, having been subdued by the second Muru Muru, is herself imprisoned in a sphere, though she preserved Yuno's memories by consuming her body. The first Muru Muru establishes contact with the third Yuno, giving her the memories of the first Yuno. By the time Yuno reunites with her old friend, Muru Muru has taken on several of Yuno's physical traits, including her signature pink hair. Deus and the third Muru Muru monitor the reunion, Deus concluding that absorbing Yuno's memories allowed Muru Muru to come to terms with both her own sins and Yuno's suffering, and sought redemption. Yuno frees Muru Muru, who helps her break into the then-empty second world to meet with the second Yuki, reuniting the couple at last, along with her bored second world self, who spent 10,000 years in limbo with a depressed Yuki and a rotting manga book for company.
In an alternate twist of events, before the second survival game is due to start, Muru Muru absent-mindedly is making mucho in the Cathedral of Causality when she ends up smashing a hole in the causality itself. Muru Muru investigates the damage, discovering she has erased Yuno from existence. As Deus declares the start of the survival game, he realises Yuno is absent. In a panic, Muru Muru leaves the cathedral to temporarily take Yuno's place until she can fix the damage she made.
On the second day of the game, Yuki is thrilled to have his diary but is shocked when he sees Muru Muru dressed as Yuno, trying to copy Yuno's stalker-like actions. Muru Muru begins to make mochi in class and is promptly sent outside by the teacher. It turns out Muru Muru is trying to make a stick of mochi in order to capture Yuki so he is not murdered by Takao Hiyama. Muru Muru approaches Yuki, imitating Yuno, and chases him with her mochi stick to capture him. As Muru Muru chases Yuki, Hiyama joins the chase with the goal of killing Yuki, the chase leading to the office building where Hiyama is meant to be eliminated. Muru Muru trips and ends up getting stuck in the mochi. As Muru Muru flies up to the fourteenth floor, only to witness Yuki being stabbed by Hiyama. As Hiyama goes to break Yuki's diary, Aru Akise appears with Muru Muru, Akise immediately falling in love with Yuki.
Akise agrees to help Muru Muru protect Yuki and engages Hiyama in a fight. Hiyama tries to stab Akise with his machete, unable to comprehend why he does not appear on his Murder Diary. Akise steps aside, revealing Hiyama has stabbed a fusebox and is electrocuted, killing him. Akise asks Muru Muru to help Yuki, who agrees, placing Yuki in a special bed which will heal his injuries and fix the hole Muru Muru made. Muru Muru gives Yuki's phone to Akise, attaching a small keychain Yuki doll to it to allow Akise to use Yuki's Random Diary. Thus, Akise and Muru Muru the temporarily First and Second of the survival game until the causality is fixed.
During Minene's attack on Sakurami Elementary School, Akise and Muru Muru must perform Yuki and Yuno's actions to defeat the terrorist. Muru Muru puts on a pair of rocket-accelerated rollerskates and pulls out a syringe designed to subdue Minene. Akise and Muru Muru navigate their way through the school building as it slowly explodes, but Akise keeps going different directions and Muru Muru continues to be caught in explosions. It is revealed in a flashback that Akise told Muru Muru he wanted Yuki to become God, considering to stand in for him for the whole game until he wins by default. Muru Muru recovers from another explosion but discovers her syringe has shattered. Akise and Muru Muru step outside to confront Minene, Akise revealing he has placed one of Minene's timed bombs in Muru Muru's backpack and sends her flying through the minefield towards Minene. Muru Muru shouts at Minene to turn off the bombs, but Keigo Kurusu appears, shooting bullets at Minene.
Muru Muru flies towards Minene as the bomb's timer hits zero. Muru Muru braces herself for the detonation, but no explosion comes. Opening her eyes, Muru Muru spots Minene fleeing on a motorbike. Akise comes over and reveals he removed the bomb's gunpowder, and everything was a bluff. Muru Muru is astonished that she was tricked, and begins to ponder whether or not she can truly trust Akise or not.
A few weeks later, Muru Muru, Akise and Kurusu are summoned to Tsubaki Kasugano's Omekata temple to remove the captured Minene. Muru Muru warns Akise not to interfere with the predicted timeline. Muru Muru points out Funatsu and explains the true sins of the religion. Muru Muru skips off to get food, prompting Akise to change the future for Tsubaki, the Fifth diary owner Reisuke Houjou, Orin Miyashiro and Seventh diary owner Ai Mikami. Akise approaches Ai and Orin, convincing them to help him rescue Tsubaki from her predicted Dead End and her fate.
Approaching Tsubaki with the proposal of "elopement", Akise manages to spirit Tsubaki away from her followers and Funatsu. Akise tries to flee the temple with Tsubaki, but is spotted by Muru Muru who is having lunch with Kurusu. Funatsu confronts Akise, but Akise makes his escape thanks to an explosion caused by Orin and Ai. Muru Muru appears, warning Akise to stop altering the future. Akise ignores her and escapes with Tsubaki in the car of Reisuke's parents. Realising Akise has completely altered the future by rescuing Tsubaki, befriending Reisuke, etc. and concludes she must remove Akise's influence before it is too late.
Muru Muru takes Funatsu prisoner with help from Yomotsu Hirasaka in order to put an end to Akise and Tsubaki's alterations. Muru Muru gloats about her plan to have Tsubaki eliminated by her own hypnotised followers, plotting to kill Yomotsu afterwards. She fails to notice Yomotsu receiving a new entry on his Justice Diary. Akise and Tsubaki are captured by the followers and brought before Muru Muru and Funatsu. Tsubaki goads Funatsu into confessing that he murdered her parents, just as Reisuke turns on the temple's sound system, so that all the followers can hear him, Yomotsu ending the hypnotism after finding Reisuke and learning of the situation. Muru Muru is so enraged by Akise's deception once again that she blasts hole in the nearby roof and flies off, promising to get Akise back.
In another flashback, it is revealed that Muru Muru uses a giant robot named Mecha-Muru Muru to transplant her memories onto reality, which will fix the hole in the causality. In the present, with only an hour to go until Yuki is healed, Muru Muru is confident that her victory is assured. Akise suddenly charges through the Cathedral of Causality on an elephant, planning to find out Muru Muru's true goal by looking in the memory bank of Mecha-Muru Muru. Noting how Muru Muru knew how the survival game would develop, Akise makes his way towards Mecha-Muru Muru, only for Hiyama to appear, Muru Muru revealing she resurrected him to ensure that the survival game can start anew correctly. Akise lands on Mecha-Muru Muru's head, only to find a brainwashed Yuki waiting for him, armed with a knife. Yuki stabs Akise with the knife, designed by Muru Muru to erase Akise's memories. As Akise despairs, he is helped up by Tsubaki, discovering she, Reisuke, Orin, Ai and Marco Ikusaba have come to help him.
Marco gets into a fight with Muru Muru, whilst Reisuke fights Yuki. Tsubaki accompanies Akise to the memory bank entrance, convincing him to go through the entrance door. In Muru Muru's memories, Akise finds himself in Yuno's house. Hearing Muru Muru speaking to Yuno, Akise peeks through a door to the room where Yuno's parents died, discovering Muru Muru giving Yuno her second Future Diary whilst the second Yuno lies dead on the floor. It is at this point that Muru Muru fixes the hole she made and the events of Paradox are erased from existence.
- Muru Muru is named after the Goetic demon Mur Mur.
- Muru Muru's character theme song is "Ubiquitous" by NIRGILIS.
- The white number in Muru Muru's forehead is referring to the world number.
- By the end of the manga, it is revealed Yuki and Yuno stayed together through a further four timelines, revealing they gained seven Muru Murus for company.
- In one of the shorts Muru Muru has a type of candy that allows her to change her age at will.
- Muru Muru's character does not exist in Future Diary: Another World, instead composited together with Deus Ex Machina to create the serial's version of Deus.