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Ruki Mukami (無神 ルキ Mukami Ruki) is the oldest son of the Mukami household. He is known as the 'Brains' of the Mukami family.
Ruki is a handsome young man with short ruffled hair colored with black on top and white on the tips. He has blue-grey eyes and also three black piercings on his right ear. Ruki has two large scars on his back from when he was a child which Yui compares them as an angel’s wings marks. He wears black web chokers on his neck. He is often seen carrying a book in his right hand.
He usually wears a grey jacket with a long sleeve black shirt underneath and wears it with black pants and a brown belt. He sometimes wears a long-sleeved maroon shirt with a black butterfly print on the bottom left side and wears it with black pants and a black belt. He wears the black web chokers with both outfits.
His school uniform consists of the black school jacket with a white dress shirt that is slightly unbuttoned revealing a long-sleeved maroon shirt underneath and a long black tie over it. He wears it with the black plaid uniform pants and brown shoes.
In the sixth game LOST EDEN, Ruki's school uniform consists of the dark red school blazer with a white dress shirt and he wears a long-sleeved maroon shirt underneath. He wears black pants and white shoes.
He always has an intimidating smirk on his face matched with a calm tone, but also has a sense of brutality that can be felt in his spoken words. Without dirtying his own hands, he interacts with others as a cruel-hearted military do-S (extreme sadist). Ayato tends to mock him for his sometimes forced intellectual manners.
Ruki likes to view and treat Yui like livestock, not only because she is a human and he a sadistic vampire, but also because in his past he was treated that way by the stronger grown-ups in the orphanage he lived in. It is also due to his trust issues towards women after he was abandoned by his mother.
Before he was turned into a vampire, Ruki was a human born into an aristocratic family. He was a spoiled and arrogant little boy who found amusement in treating other people harshly and sadistically. However, as karma would have it, Ruki’s father, a kind and generous person, wasn’t good at managing his business and became bankrupt. It is later revealed in LOST EDEN that the cause of his father's bankruptcy was a devil named Trismégiste. He manipulated the President of the country into embezzling the public funds, imposing high taxes and even dismissing the aristocrats and politicians (among them was Ruki's father) who supported him.
Ruki only found out about this when he woke up that morning to the servants ransacking the house for valuables. He tried to stop them, but they banded together to beat Ruki up for all the cruel things he did to them while telling him about the state of his family. To make matters worse, they told him that his mother ran off with a secret lover, leaving only a letter saying that she loves him. After the beating, Ruki went to the garden and found that his father had hung himself.
Ruki stayed behind in his family home for some time, hoping that his mother would come back.(He even wondered to himself how his mother could say she loves him but leave him behind, which caused him to develop trust issues towards women and their capability of loving him). Before he gave up and had to live on the streets, mocked by another aristocrat. He ended up in an orphanage where he was bullied by the other orphans and mistreated by the caretakers since he was a former aristocrat with a bad attitude.
However, the only people at the orphanage who were kind to him were fellow orphans; Kou, Yuma, and Azusa. He met Azusa first after being bullied one day, and Azusa took an instant liking to him for being covered in cuts and bruises. He followed Ruki everywhere in order to get beaten up alongside with him which initially creeped Ruki out. No matter how many times Ruki tried to push Azusa away, Azusa never left him alone. He didn't care whether Ruki was a former aristocrat and he told him that receiving physical pain was another way of forgetting your emotional pain. Ruki started seeing Azusa like a younger brother and the two became friends. He later on met Kou and Yuma and became friends with them as well.
The four of them eventually devised a plan to escape their "hell". Unfortunately, while the plan started off well, they were pursued and caught by the orphanage staff who shot them. Even though Ruki wasn't shot himself, he was branded on his back like ‘livestock’ as punishment for being the mastermind behind the escape plan. As Ruki believed he was at the deepest pits of hopeless rage and despair at the world, Karlheinz appeared and offered the four children the chance to become vampires in order to take revenge on the world that, in his words, deprived them of everything if they agree to serve him.
Ruki, Yuma, Kou, and Azusa became vampires and brothers. Karlheinz chose Ruki to be the ‘brains’ of the group, making sure that he was well-educated and capable of leading his brothers. When he asked why Karlheinz chose to give him all this education when the others didn’t have that, Karlheinz told him that it was Ruki’s new role and that they’re all necessary for his plan. The plan details a human girl "Eve" with the heart of the demon lord’s daughter. "Eve’s" blood would choose an “Adam” who would be able to obtain the power to control the world, and their descendants would change the world. Ruki felt indebted to Karlheinz, so he worked for him, doing what was needed to help him complete that plan.
Ruki is the eldest son of the Mukami household. Granted by Karl, his job is to be the leader and look after his younger brothers: Kou, Yuma, and Azusa. Unlike the Sakamaki brothers, they have a closer relationship with one another and care for each other. His younger brothers respect him and follow his lead. Ruki's strategical thinking helps them to fight and cover each other's backs even against stronger opponents. This is demonstrated in Azusa's DARK FATE route when he and his brothers worked together to save Yui from the First Bloods. His mind helps him usually strategies and overcome the strength gap between them and pure born vampires, and even makes them survive and escape a direct attack from the First Bloods.
The Mukamis love to have dinner together and they all praise Ruki's cooking. Ruki is talented in cooking especially in making soups. If the boys start arguing on the table, Ruki is the one to put them all in order, even though sometimes Yuma's free spirit makes the two males clash at least verbally. All of them deeply respect one another and always help each other. Even if not sharing blood ties, the Mukamis have very strong family bonds with each other.
Ruki respects Karlheinz since he is the one who gave them a second chance at life, along with his brothers, thus saving him from the orphanage, or as he dubs it, "Hell". He feels indebted to Karlheinz, so he agrees to work with him for the "Adam and Eve" plan. Ruki has never fooled himself that Karlheinz does this out of "good heart" even though he respects him deeply and obeys him. He does want to know Karl's true intentions but would never question his decisions.
When he began to realize that an impure vampire like him can never become "Adam", Ruki began to feel conflicted. A part of him one did not wish to ever betray Karlheinz, while his other side did not want to give up the newly discovered bond and the so-intoxicating blood. However, in Ruki's vampire ending in MORE BLOOD, he decided to betray Karlheinz in order to be with Yui. He claims that rather than "Adam", he is the "snake who tempts Eve", but she agrees to be with him despite what he believes.
In DARK FATE, it is revealed that Ruki requested Karlheinz to introduce him and his brothers to "Eve" (prior to the start of MORE BLOOD). As there was nothing happening between Yui and either of the Sakamaki brothers (Karlheinz's sons), he told Karlheinz that he and his brothers will become "the snake who tempts Eve". They will force an "Adam" to awaken amongst the Sakamaki's by sparking a catalyst that will ensure that "Eve" will be instantly bound to an "Adam". However, he later questions his initial intentions and his loyalty towards Karlheinz when he falls in love with Yui. Even though Ruki keeps being unfit to be an "Adam", Karlheinz's experiment takes the turn that makes it possible for Ruki to become a human again.
He was saddened by Karlheinz's death in LOST EDEN, and was conflicted to learn that the man who saved him and his brothers, was also the man who caused his biological family to fall to ruin.
Ruki is very strict with Yui. Right off the bat, he forces her to sleep in his room so that he can monitor her at all times, thus giving her limited rights. He also forbids her to go to school since the Sakamaki brothers go there, but he eventually allows Yui to attend school normally. However, even at school, he still monitors her by making her attend his lessons. When Yui gets attacked by Ayato, she tries to keep quiet about it, but Ruki sees right through her and he bites her in the stomach as punishment. Yui once brought home a stray kitten, but Ruki kills it which upsets her. Finding it unbearable to see Yui upset, he hugs her from behind to cheer her up. One night, Ruki has a nightmare. Yui tries to comfort him, but he loses control of himself and almost strangles her. When he regains his senses, he kicks Yui out of his room to ensure her safety. When Ruki and his brothers find out that Ayato has discovered their whereabouts, he locks Yui in the dungeon to protect her, and because of his impatience to become "Adam". After some time and with persuasion, he releases Yui from the dungeon, but his time with her is short-lived when Ayato flies in out of nowhere and knocks him out with a punch. It is hinted that Ruki does actually care for Yui when he grabbed her hand in an attempt to stop Ayato from taking her away. After some time passes, Ruki visits Yui one night, and he tells her about his past in better detail than before, as well as the "Adam and Eve" plan. He then wishes her farewell since he has finally realized that he can't become "Adam" and he encourages her to choose one of the Sakamaki's instead. By then, Yui has realized that she has fallen in love with Ruki. However, in his Vampire Ending, he admits that he regretted letting Yui go and decides to betray Karlheinz in order to be with her.
In Ayato's MORE BLOOD route, he appears more friendly, gentlemanly and caring towards Yui, unlike in his own route. He tries to convince Yui to leave Ayato and to come with him instead, but she tells him she can't trust him. This prompts Ruki to attack her and suck her blood by force. When Yui "leaves" Ayato, Ruki meets her the in the forest along with his brothers and they take her back to their mansion. However, Ruki declines Yui's blood when she offers it to him after he got stabbed by Ayato. He explains that he wants to wait until her heart has chosen whom to follow and will not hesitate to make her his if she chooses to be with him. After Yui finally realizes her feelings for Ayato, she visits Ruki in his mansion to turn him down and he reveals to her that he was not being serious at all, it was only an act. However, in Ayato's Brute Ending, Ruki finds Yui wandering through the city streets upset about the fact that Ayato won't touch her or drink her blood. He approaches her saying she seems to have become accustomed to having her blood sucked multiple times. He then asks her if she would like him to replace Ayato though he considers it provoking to be a substitute.
He plays the antagonistic role in Ayato's MORE BLOOD route. When Yui passed out after Ayato forcibly sucked too much of her blood, he helped her to the infirmary causing Ayato to get irritated to find him with her. Whenever Ruki met him face-to-face, he took the opportunity to taunt and provoke him about his feelings towards Yui which Ayato fiercely kept denying. Towards the end of the Ecstacy chapter, Ruki went overboard with his taunts which provoked Ayato who stabbed him in a fit of rage. Depending on the player's choice, Ruki voluntarily covers up for Ayato when he was asked how he got stabbed. Ayato also got annoyed when Yui visited Ruki at his mansion in order to properly turn him down. In Ayato's Brute Ending, he is killed by Ayato who found him drinking Yui's blood to satisfy her masochist desires.
In his MORE BLOOD route, when Ruki asked Ayato if he's reclaiming Yui because he loves her, Ayato laughs and says that Yui's blood is only delicious. Hearing this, Ruki tells Ayato to leave without Yui, because he cannot hand her over to him.
Like all vampires, he has an inhuman strength as well as increased speed (less than a pureborn vampire), increased vision and hearing, and smell. Being a vampire, he also has fast healing though it is slower than a pure-bloods.
He appears to be capable of teleporting from nowhere in an instant.
He is very intelligent and is strategical in combat.
Impure vampires do not have the same amount of skills like pure ones, nor do they possess their own magic, however, Karlheinz borrows some for them, such as protective barrier and bat familiars.
However, due to being former humans they are quite used to things like daylight and human food.
- He is right-handed.
- His foot size is 27.5 cm.
- The book he always reads is a memento from his father.
- In MORE BLOOD, he is rivals with Ayato and likes to taunt and provoke him when it comes to Yui.
- His recent interest is making original dishes or recipes.
- He hates strong-flavored food and drinks.
- He is skilled at cooking and even knows how to flambé.
- He knows how to ride a horse.
- He is fluent in Nordic and proficient in English.
- Ruki and Yui have a son named Adam. Later, Adam appears to be a first blood and Shin Tsukinami's son.
- He becomes Shu's right-hand man (only in his route).
- In Episode 17, he is shown to be reading The Catcher in the Rye.
- In CHAOS LINEAGE, he is the leader of the Orange Family.
- Diabolik Lovers More Blood; Ruki's Route, Dark Epilogue
- Diabolik Lovers More Blood; Ruki's Route, Ecstasy Prologue
- Diabolik Lovers Dark Fate; Maniac Epilogue
- Diabolik Lovers Dark Fate; Ruki's Route, Maniac 01
- Diabolik Lovers Dark Fate; Ruki's Route, Maniac 06
- Diabolik Lovers Dark Fate; Ruki's Route, Brute Ending
- Diabolik Lovers Lost Eden; Ruki's Route, Vampire Ending
|Sakamaki Brothers||Ayato Sakamaki • Kanato Sakamaki • Laito Sakamaki • Shu Sakamaki • Reiji Sakamaki • Subaru Sakamaki • Kino|
|Mukami Brothers||Ruki Mukami • Kou Mukami • Yuma Mukami • Azusa Mukami|
|Tsukinami Brothers||Carla Tsukinami • Shin Tsukinami|
|Others||Karlheinz • Beatrix • Cordelia • Christa • Richter • Seiji Komori|