Rui Arneb

Louis Arneb (ルイ・アルネブ) is a Sin Archbishop of the Witch Cult, representing the Satiation aspect of Gluttony. First introduced in Arc 5, she later served as one of the main antagonists of Arc 6, alongside her brothers, Lye and Roy. She later becomes a supporting character in Arc 7.

After a chance encounter with Natsuki Subaru, she learned of Return By Death, ate his memories, and possessed him using a copy of herself in order to gain his authorities. However, Subaru ultimately managed to defeat her and left her for dead during the events of Arc 6, though she is later revealed to have survived at the cost of amnesia herself; bearing a completely new personality. She was transported along with Rem and Subaru to Vollachia at the end of Arc 6. Despite seemingly losing her original personality, she retains her Authority, making her status in regards to her position within the Witch Cult unclear.

Appearance
In contrast to her brothers, Louis has large blue eyes, light skin, and extremely long blonde hair that can cover the floor like a golden sea. However, as is the case with Lye and Roy, she has fang-shaped teeth which help her smile look to be one more reminiscent of a menacing smirk. She is physically in her mid-teens, although her exact age is unknown. During Arc 7, her hair is tied back in a ponytail after Subaru is reunited with her and Rem.

Louis's debut featured her in her brother Lye's black cloak that was tied just below her neck with uneven tears along the lower portion. However, in Arc 6, she presents herself in an elegant white dress close to looking transparent. It comes with a jabot that has two small red lines along the leftmost side. This look is maintained after she leaves the Corridor of Memories.

As Louis's physical self had been trapped within the Corridor of Memories until Arc 6's climax, she occasionally possessed the bodies of her brothers in order to experience the outside world.

Personality
Subaru describes her as a girl that'd look good with a smile, yet he describes her "smile" as a smirk, and gave off the feeling that she made light on the lives of many people. She is also described to be evil intent in the shape of a child. Louis doesn't care much about what she eats, putting more emphasis on who she wants to eat, befitting of her role as Satiation. Also, the three speak in a collective manner using us and we instead of first or third person.

Being the youngest sibling, Louis initially​ gave off the impression of being respectful and loving towards her brothers, but later reveals that she found them idiotic for blindly eating lives for her just because she was unable to exit the Corridor of Memories. Louis believed that life was unfair in a manner similar to that of a conveyor belt, without having the ability to choose the family, environment, and future to be born into. Because of these beliefs, Louis developed a goal of searching for, devouring, and becoming someone else all in the name of happiness, which would have allowed her to live with her head held high in a life she considers "ideal".

In her desire to achieve a happy life for herself, Louis was very shrewd, claiming that Subaru helped Emilia, Beatrice, and Rem out of pity. She even claimed that he did it all for his own gratification as part of her plan to get him to reject the existence of ‘Natsuki Subaru’.

After experiencing Return By Death, the Louis that had entered Subaru as a Witch Factor became traumatized and got into a fight with the Louis within the Corridor of Memories, who retained her original personality. The end result of this confrontation was that Louis lost her original mind, regressing into an infant-like state.

After mysteriously materializing outside of the Corridor of Memories, Louis's mind deteriorated into an infantile state. She is currently incapable of speech and complex thinking, instead displaying a mind driven by instinct similar to an animal's. Interestingly, she seems to have an amicable inclination towards Subaru in this state, despite his previous actions against her. She would even go as far as to affectionately lick his face and protect him when others threatened his life, as was the case when she tackled Rem when the demon girl tried to strangle him. Even after Subaru treats her badly, Louis continues to act friendly towards him.

History
Since her birth, Louis was confined in the Corridor of Memories. Despite being the younger sister of Lye Batenkaitos and Roy Alphard, they were unaware of her existence. Due to her confinement, she only found satisfaction in the occasional "meals" that she was able to receive from her brothers which came from the effects of the Authority of Gluttony. Later, she found a way to temporarily escape by possessing the bodies of her brothers, which made them aware of her existence. She later gained access to Eclipse after her brothers discovered it and used it to devour people in her search for happiness.

Abilities
Authority of Gluttony (暴食の権能 Bōshoku no Ken'nō): Louis is able to use the Authority of Gluttony.
 * Gluttony (暴食 Bōshoku): Louis can eat the name and memories of an opponent. To eat a name, she touches them with her left hand, then licks the palm of the same hand. Things such as experience, talent, and the likes and dislikes of human relationships serve as food for her, allowing her to take advantage of any abilities or memories her opponents had. However, if she eats a fake name, she becomes plagued with severe nausea. Even after killing Louis, the names and memories of the forgotten will not return to their original owners.
 * Those that have had their names eaten have their existences erased from the world, destroying any human relationships along with negating any contracts with Spirits.
 * Those that have their memories eaten become amnesic and any characteristics they may have had are reset, effectively making them into a different person.
 * Those that have both their name and memories eaten simply become a shell, and although they live, they no longer eat, excrete waste, or age, putting them in suspended animation.
 * She cannot eat the same person twice until that individual gains enough new memories to establish a different sense of self from their old one.
 * Eclipse (蝕): Eclipse is considered to be the trump card of Gluttony. It is divided into two types; Solar Eclipse (日食 Nisshoku) and Lunar Eclipse (月食 Gesshoku).
 * Lunar Eclipse allows the holder to use their victims' memories and harvest their skills and knowledge. Lye, for example, used Lunar Eclipse to greatly boost his physical strength and perform numerous martial art techniques including The Palm of the Fist King and the Leaper technique. It is worth noting that by eating a person's name and using Lunar Eclipse, Louis does not gain her victims' Divine Protections or Spirit Arts.
 * Solar Eclipse allows the holder to harvest their victims' name and transform their appearance accordingly. Louis, for example, transformed into Neiji Rockheart and numerous other victims she and her two brothers had eaten throughout the years, using her sibling's body. Both Lye and Roy dislike having Solar Eclipse used on them. According to them, Solar Eclipse made them feel as if their selves were being damaged, making it unendurable. Unlike Lye and Roy, Louis tends to primarily use Solar Eclipse as she doesn't share the same fear as her two brothers.
 * Demon Beast Control: Because Louis, Lye, and Roy each possess the Witch Factor of Gluttony which was previously in Daphne's possession, they can direct Demon Beasts to attack certain areas. This is why the Hakugei's attacks were coordinated with those of the Witch Cult. Despite her ability to control the Hakugei and the Oousagi, even if Louis had help from her older brothers, they wouldn't be capable of controlling the Kurohebi, according to the author.
 * Creation: Louis stated she and her brothers can create life with the usage of her Witch Factor of Gluttony, just like how Daphne created the Demon Beasts four centuries ago. However, Louis has also stated she and her brothers had no reason to do so, hence they never followed through the idea.

Master Class Fighter: Through the accumulation of souls eaten with her Authority, Louis gains any abilities her victims once had such as martial art techniques and magic by using Lunar Eclipse. In turn, this grants her extraordinary combat strength.


 * Leaper Technique: This technique allows Louis to move with extreme speed undetectable by the naked eye, essentially allowing her to leap behind his opponents or avoid extremely precise and quick attacks. Due to the extreme speed, it seems like she's teleporting around the battlefield. She's also capable of utilizing it vertically, making it appear as if she's flying. This move originally belonged to Dorkell.
 * Carnivorous Beast: In the Web Novel, Louis displays the aforementioned ability which allows her to strengthen her body which gives her two advantages: She can withstand powerful attacks, and she can strengthen her limbs to deliver devastating blows. With this ability, she was able take a hit from Emilia's ice spear and came out unscathed. She was also able to deliver a retaliatory punch that was said to be as devastating as getting hit by a car. This ability formerly belonged to Beli Hainelga.
 * Unnamed Earth Throwing Technique: In Arc 7, Louis utilizes an unnamed earth throwing technique to repel a group of horned demi-humans. When peeling off chunks of nearby walls or concrete, it’s mentioned that the earth takes on a softer texture and is peeled away as easily as lifting up a carpet. When thrown, it regains its usual hardness.

Splitting: Similarly to the Oousagi, Louis can split and create a copy of herself whenever she separates her Witch Factor of Gluttony into multiple pieces. With a copy, Louis can not only attach herself to someone else as a Witch Factor, but she can also gain the ability to take control of their body whenever she wants. In Arc 6, Louis used this ability to attach a copy of herself to Subaru, which allowed her to forcibly trap his memories up to that point within the Corridor of Memories, and with the amnesiac Subaru, she occasionally possessed him while pretending to be his "original self" in order to instill distrust and paranoia within him. Louis can split and create more than one copy of herself, but it is not known if there are limitations in the amount of copies that she can create.

Trivia

 * Like the other Sin Archbishops (with the exception of Stride Vollachia), Louis received her namesake from a celestial body. "Arneb" was a former name for Alpha Leporis, the brightest star in the Lepus constellation. The word was derived from the Arabic term أرنب (arnab), which translates to "Hare".
 * In a Q&A, the author stated that if Daphne and a Sin Archbishop of Gluttony were to fight, it would most likely end in a draw. It is unknown if this answer was stating that a fight with Louis and her siblings would end in a draw against the Witch of Gluttony if they fought her all at once, nor is it known if the resulting draw would only come from a match with one of them.
 * In Arc 6, Louis has her own named chapter in both the Web Novel and the Light Novel.