Shirahime

Shirahime/Sidero, also known as Sidero of the Demon Sword Murasame, is a fallen angel and one of the Demon King's generals. After her and Lucifer's defeat at the hands of Hero Emilia, they were secretly rescued by Olba Meyer, who promised to return Sidero and Lucifer to heaven if they became allies in defeating the Demon Lord. After being defeated by the Demon Lord, she and Lucifer moved in with Sadao Maou and Ashiya. She and Lucifer are twins.

She eventually obtains a second sword called Yatsufusa, which gives her the ability to create corpse dolls which later adds to her personality.

Appearance
In human form, Sidero appears as a young girl with long black hair that reaches down to her knees and red eyes. She wears a dark sleeveless mini dress with a white collar and a red tie; she wears a red belt that has a red side skirt cover. She wears it with long black socks and black shoes. She also wears red gauntlets and black gloves. She sometimes wears a long dark coat in battle. She is often seen carrying her Teigu, Murasame. After activating Murasame's trump card, she has faded red scars all over her body.

When she regains her powers, Sidero gains a pair of black, feathery wings. After repeated consumption of Suzuno's Celestial Force imbued cooking, Sidero's wings momentarily regain their white color. Her hair and eyes also changed to purple, which was her original hair and eye color.

Personality
Although she shares some traits with her brother, such as her social awkwardness and a big appetite, Sidero is much more aloof and seems to show darker sides of her when it comes to killing her enemies. She is cold and ruthless in battle, usually ending the lives of her enemies as one would expect from a seasoned assassin.

Secretly, she is very scared of being seen as weak, knowing that, in the Demon Army, if she became dead weight she'd be taken out to keep her silent. This has a lingering effect of her upbringing, as she almost did suffer this fate.

She cares about her comrades very much and she is always worried that one of them may not make it out alive due to her experience that the war always has a high mortality rate.

She also tends to hide her emotions when it is revealed that a comrade dies, making Lucifer mistakenly and incorrectly assume that she deals with it easily, because she is used to it. However, this prompts her to break into tears saying that she can never be fine when she loses a friend, for it is the most horrible thing of which anyone can experience. She is then comforted by a sorry Lucifer who resolves to not die and never let her experience such pain again, making her smile.

She is good with technology and loves playing video games, mainly with Lucifer. Sidero also has a slightly sadistic side to her, which she usually keeps hidden. Lucifer still can't help but be shocked every time he sees his sister act that way.

Before the destruction of her second Teigu, Yatsufusa, she displayed an unstable mental attachment to her fallen comrades as she kept them as her corpse dolls, as shown with Run. When he was severely injured and about to die, she stated that it allowed them to be "together forever", and she intended to add her brother to this collection. She also seemed to play with the corpses of those she has killed, as well as keeping powerful ones to use in her permanent collection, which is limited to eight.

Sidero loves to eat and is surprisingly known to be a big eater (she usually prefers meat and fish), much like her brother Lucifer. She is passionate about food to the point that Lucifer noted how the "usually cool" Sidero turned mad when she had burned some meat.

Sidero is extremely close to her brother, to the point of requiring him to be by her side in order to function correctly. If Sidero is separated from Lucifer by so much as a closed door, she becomes almost catatonic until he returns to her. This can generate problems as when Sidero bathes; she does not want Lucifer to see her naked yet she can't be separated from him far enough to not be seen. This can be resolved with the presence of steam to cloud their view enough. However, Sidero also generally dislikes bathing as it stiffens her hair.

Following the end of the war, Sidero is shown to have been affected by a sort of PTSD. She is shown to be a lot more demure and depending on others, especially Wave and Lucifer, the latter of whom she genuinely cares for and loves. At times, she hallucinates seeing her former corpse dolls vengefully approaching her, to which she is immensely remorseful.

Hanzō Urushihara
If he is separated from Sidero by so much as a closed door, he becomes a spineless, cowardly wreck and only returns to his former self if he is able to see or hear her. He views his sister as his equal and partner and even looks up to her, but is also protective of her, such as putting his body between her and the ground when he thought they were going to crash after being defeated by the demon lord. She confides in him, and he, in turn, goes out of his way to ensure that she is not upset. He often acts like a worrying mother towards her, showing excessive concern whenever he thinks she is in trouble.

Despite being arrogant, manipulative and cunning, he loves his sister dearly (to the point where they can't be separated).

Sadao Maou
Sidero once served under Satan as one of his Demon Generals with Lucifer. She was thought to have been killed by Emilia, but showed up in Japan with Lucifer and Olba, scheming to kill both Maou and Emi. When she failed to do so, Maou took her and Lucifer in to prevent them from being discovered by the police. Ever since than, she has been in his dept and uses polite language when addressing him. In turn, Maou respects Sidero and admires her fighting abilities, most of which comes from the fact that she is much more mature than Lucifer. She is, however, oblivious towards his romantic feelings directed towards her.

Shirō Ashiya
Together with Alciel, Adramelech, Malacoda and Lucifer, Sidero was one of the five demon generals appointed by Satan. After arriving on earth and encountering Sidero and Lucifer again, Ashiya was shot by Sidero and Lucifer when the latters attacked Japan, but was able to join the fight against them after being aided to recovery by Maou.

After moving in with Maou and Ashiya, Sidero, unlike Lucifer, was treated with respect and often called "Sidero-San" by Ashiya. He likes cooking for her and safely assumes that Sidero really likes food as that, in his imagination, she's always eating some sort of snack.

Wave
They were friends to an extent, and play chess together during their free time. Though she does not talk much, Sidero is usually seen walking with Wave. Whenever Wave's attempt to comfort a teammate fails, she pats him on the shoulder. Their relationship has developed further following Sidero's assassination attempt; she confides her fear of being killed for being weak and useless to him, and thanks him for his concern.

Seryu Ubiquitous
Whenever Seryu and Sidero were seen together, they appeared to get along just fine, fighting well alongside each other and sometimes sharing sweets. After their first meeting, Seryu even allowed Sidero to play with Koro.

Green
Sidero is aware that Green is in love with her, but doesn't return his feelings. She does value him as a friend and comrade. This is shown when she reanimated him as a corpse doll using Yatsufusa.

Guy
Sidero didn't like Guy's perverted antics and even kicked him in the face when he tried to see up her skirt. She later avenged his death by killing Weneg.

Run
Run and Sidero worked together to get revenge on Ente Isla. They displayed great teamwork and loyalty to one another, as he is able to save her multiple times. When he was about to die, Sidero could not bear to lose her comrade, so she turned him into a puppet.

Bols
Sidero and Bols had a friendly relationship for being members of the same team. Both were targeted for assassination, and Bols was killed. Sidero became enraged and ordered her puppets to brutally kill Chelsea for Bols' death.

Leone
Sidero and Leone appear to be good friends (Leone even considers Sidero to be her best friend), but their relationship is sometimes used for comical effect, as seen when Leone punches her when she comments on the difference in their weight. Leone tells Sidero that she is her best friend shortly before parting ways, whereas she dies afterwards.

Sataniel
Sidero is Sataniel's daughter. After finding out about Ignora's actions, Sataniel took her and Lucifer, fleeting from heaven.

Ignora
Ignora is Sidero and Lucifer's mother. She experimented on her and Lucifer while they were still in her womb, which made them immortal.

Demon Magic
On Earth, she ends up in similar circumstances as Maou and Ashiya. Her powers are limited, and has to feed off the negative emotions of humans in the surroundings to regain her powers. Just like Maou and Ashiya, she has her own unique demonic aura, and that color is red.
 * Satanic Force: With this power, she possesses and is able to utilize strong demonic power. This ability not only grants Sidero great strength and control over numerous variations of demonic abilities, but also allows her to overwhelm weaker demons as well as rival that of powerful demonic entities. If used incorrectly, this power may corrupt her and, on extreme levels, could kill her.
 * Flight: Sidero can summon black wings to fly at great speed. They seem to only manifest when she has harnessed enough power from negative emotions.


 * Explosions: When Emi landed on a streetlight, one of her black feathers floated down beside her and exploded before Emi could react to it. The limitations of this ability are unknown.


 * Energy Projectiles: Just like Lucifer, she is able to fire red colored projectiles that can either pierce or explode upon its contact.
 * Demonic Aura: Sidero can surround herself in wretched demonic energy. It is impressively destructive and more potent than regular auras given that demons are stronger than most beings.

Teigu: Murasame
Sidero carries the Teigu, One-Cut Killer: Murasame, a katana known for being coated in an immensely deadly poison that could kill those cut by it within seconds, as the poison itself had no antidote. The Teigu's trump card, the ability to strengthen its user with the power of its poisonous curse for a short amount of time, was revealed during the final battles. It is revealed near the end of the manga that Murasame's poison could only target one life at a time.

Teigu: Yatsufusa
Sidero eventually gains an offensive Teigu, in the form of a sword named "March of the Dead: Yatsufusa", which allowed her to enslave up to 8 enemies killed with the Teigu. However, the corpses did not show any emotion.

Intelligence
Sidero has shown to be a genius with an almost supernatural intelligence, with incredible scientific calculation and simulation abilities. Like her brother, she possesses eidetic memory and is able to learn and recall a vast amount of information quickly and accurately. Lucifer has stated that she has beaten a chess program written to beat a grandmaster twenty times in a row, and she herself has stated that chess is no different from Tic-Tac-Toe. It has also been stated by Lucifer that she fluently speaks 18 languages, and learned to read "humanity" in 15 minutes. She is also incredibly skilled in first-person shooters due to her ability to predict the movements and bullet trajectories of her opponents. These predictions are more focused on mathematical probability rather than psychological observation and deduction, unlike Lucifer.

Technology
Sidero is surprisingly good with electronic devices, and possesses incredible hacking skills (she revealed to Emi that she hacked a human rights website in Vol. 4).

Holy Power
Despite becoming a fallen angel a long time ago, Sidero is still able to use holy magic after eating holy food for some time. This is shown in Volume 4 of the light novel where Sidero produces a pair of angelic white wings, to Maou's and Ashiya's surprise. Her hair also changed to purple, which was her original hair color before she left heaven with Lucifer.

Physical Abilities
Sidero is often considered to be one of the strongest characters in the series, slaying even the strongest of enemies with minimal effort. Her hellish assassination training allows her combat prowess to be on par with those as powerful as the General rank within the military levels of the Demon Army, Esdeath herself acknowledging her strength. Sidero is an extremely skilled master swordswoman, able to wield her Teigu Murasame with utmost dexterity and precision, able to slay numerous enemies, even highly skilled and powerful enemies with incredible ease. At her full strength, Sidero managed to hold her own against Esdeath, a tremendously powerful master swordswoman and ultimately killed her with single precise thrust, plunging Murasame's shattered blade to stabbed directly into Esdeath's heart. Sidero possesses tremendous speed, agility and reflexes, being able to dodge and counter-attack with deadly results, and is also skilled in hand to hand combat. She also gives off no killing intent at all when she fights, making it difficult for the enemy to sense her presence. She is also immune to most poisons.
 * Enhanced Reflexes: She has drastically enhanced reaction speed, allowing her to dodge bullets, catch flies in mid-air, dodge and maneuver around complex attacks, catch falling objects, block detriments and react instantaneously to what others, even the most skilled of demons, take more time to react to.


 * Immense Strength: She has strength beyond that of a normal member of her species. Even in her young and weak state, she is able to lift up debris weighing tons and that are a hundred times larger then herself.


 * Immense Speed: During her battle with the demon lord, she was able to run at immense speed, making the demon lord lose track of her for a short amount of time.
 * Superhuman Endurance: She can endure physical stresses beyond the capabilities of the greatest demons enabling her to do things such as operating on a "low power setting" (being able to operate efficiently for extended amounts of time), holding her breath for large periods of time, remain calm through stressful or painful situations, tolerate extreme hunger, unbearable thirst, and strong urges to sleep. She was also able to survive a fatal wound to the back of her neck. Sidero states that the only reliable way to kill her is to either crush her heart or decapitate her.
 * Superior Fighting Abilities: Sidero is unbelievably skilled in most known forms of fighting. She can be exceptionally proficient in the fighting traditions of a variety of cultures and become advanced with her own individual methods of close quarter combat, including martial arts (from all over the world), boxing, and wrestling. She is also superhumanly skilled in her use of weaponry, specifically swords, and assassination.
 * Enhanced Agility: Sidero can go from one motion to another effortlessly, effectively dodge attacks, swing from things easily, sprint, do back-flips, leap across rooftops, and numerous other gymnastic, athletic and martial implements with little to no effort. Agility is "the ability to rapidly respond or change by adapting its initial stable configuration", the ability to change the body's position efficiently, and requires the integration of isolated movement skills using a combination of balance, bodily coordination, speed, reflexes, strength and endurance.
 * Immortality: As the formerly second strongest archangel, Sidero has an infinitely long lifespan. The excessive passing of time does not degrade her vessel, like with all celestial beings. Her vessel is unaffected by diseases and toxins.

Quotes

 * "Demon Sunday school story? God prefers humans to angels. He gets jealous. And then he gets creative, and he tempts and twists a human soul into the very first demon."
 * "Only those who comprehend the implication of war can be capable of bearing arms."
 * "All this time, I seriously thought that its better to die than to live your life alone."
 * "If you want to kill me, you'll have to either pulverize my heart or behead me, or else I won't die."
 * "To kill the one you love. If someone else will do it anyway, I'd rather do it myself."
 * "If you can't find a reason to fight, than you shouldn't be fighting."
 * "I'll always be there to save you, because you're my brother."

Trivia

 * The name Sidero means Evil Nymph.
 * Shira is of Hebrew origin and means "song." In Japan- the name of the Grimm's famous "Snow White" is Shirahime.白姫, pronounced she-ra-he-meh in Japanese, means translated 'White Princess'. The Kanji characters for white and princess suggest 'purity' and 'goodness' – both important ideals.
 * Sidero is based off of the reaper, or death.
 * Her appearance is very similar to Akame from Akame Ga Kill.
 * Her measurements are 81-56-83.
 * It is mentioned in Volume 3 that before Sidero became a fallen angel, she was the second highest ranking angel in heaven and still wields a degree of power over lower-ranking angels.
 * Despite being a demon general, Sidero is allergic to dust and cats.
 * Apart from cat allergies, she also gets motion sickness easily (assuming she is on a long distance vehicle). Flying is apparently not an issue (Vol 5.5).
 * Shirahime shares some similarities with Imai Nobume from the anime "Gintama". They both would kill their targets without hesitation, both are very skilled swordswomen and both of them have an unhealthy obsession over their favorite foods (donuts for Nobume and meat for Shirahime).
 * In the manga, Shirahime is apparently left-handed as seen when she wields her Teigu. Interestingly in the anime, she uses her right hand.