Due to her Authority, Capella’s true form is unknown, as she can freely alter her appearance. She has taken the forms of a giant black dragon with golden horns, a small girl, a well-endowed woman, an honest-looking village girl, a swarm of field mice, and an innocent-looking young girl with a lewd smile.

In her most common appearance, Capella has short golden hair with a single strand extending down her right side, ending in a rose ornament. She wears revealing clothing, consisting of hot pants, leggings, and a bikini top. A distinctive yaeba becomes visible when she laughs. This form closely resembles members of the Royal Family of the Dragon Kingdom of Lugunica. Additionally, two large circular appendages extend from just above her waist. According to illustrator Shin’ichirō Ōtsuka’s notes in Volume 17, these appendages allow Capella to adjust her mass during transformation and give the impression that her body is composed of liquid metal.

Capella is regarded as having the worst personality among the Sin Archbishops. She speaks with contempt and cruelty, disregarding courtesy and empathy. Capella believes that all love and respect exist solely for her, reflecting her extreme arrogance and self-obsession. Even among the Sin Archbishops, known for their depravity, she stands out as a unique embodiment of malice. Viewing others as mere flesh to manipulate, she feels no concern for others’ emotions or suffering and takes pleasure in their pain, often laughing while inflicting torment.

Like her peers, Capella shows no regard for life, freely altering her own and others’ appearances to suit her desires. She ridicules and reshapes people, stripping away their dignity and identity, and has no hesitation in using corpses to create demi-beasts. Capella also holds low opinions of other Sin Archbishops, referring to them with mocking nicknames rather than by name.

True to her title as the bearer of the Witch Factor of Lust, Capella is obsessed with love and adoration, demanding affection from all living beings. However, her understanding of love is deeply distorted, driven by vanity and self-worship. She regards herself as a kind and peerless beauty, undeserving of anything less than absolute devotion.

Under the alias Mother, Capella gathers talented yet deranged individuals, calling them her children to use as tools for her ambitions. According to Elsa and Meili, she is cruel and unforgiving, punishing the smallest failures with horrific transformations such as turning followers into frogs, killing them outright, or reducing them to shapeless flesh. To Capella, her children exist to fulfill her wishes and demonstrate their love through absolute submission, which she treasures above all else.

Transformation: Capella possesses the ability to transform herself and others into a variety of beings. She can alter her voice to match her new form and modify her body at will, such as by adding wings or claws, turning her limbs into animal heads, transforming into a massive black dragon roughly the size of Priestella’s City Hall, or splitting into multiple small creatures like rats. She can also transform others into animals, including flies, frogs, birds, and beasts, or into shapeless masses of flesh devoid of senses or awareness. When she transforms a single person into multiple creatures, their consciousness is divided but shared among them. This ability also applies to herself. Capella can use her transformations for regeneration, replacing injured parts with uninjured ones. According to Al, she survived having her head severed and heart crushed. Any excess flesh created during healing dissolves afterward.

Dragon’s Blood (龍の血, Ryū no chi): Capella’s blood is said to be mixed with Dragon’s Blood, containing a powerful curse. The exact conditions for activating this curse are unknown, but simple exposure does not trigger it. She can infect others with her blood, causing black veins to appear and inducing sickness, as seen when she cursed Crusch Karsten. Reactions vary depending on the individual; while some, like Crusch, become ill, others, such as Subaru, develop a symbiotic relationship with the curse. It is unclear whether Capella’s Dragon’s Blood is the same as the one stored in the Royal Castle.

Demi-Beasts (亜獣, Ajū): Capella’s Authority extends to transforming both living beings and corpses. She can create grotesque hybrids of flesh and metal, forming monsters with weapons like axes or spears protruding from their bodies. These creatures often serve as expendable soldiers in her operations.

Storage: Capella can store and retrieve objects within her own body by altering her flesh. The full extent of this ability is unknown, though she has been shown to keep her Gospel hidden this way.

Keen Intellect: Despite her vulgar mannerisms, Capella is highly intelligent and strategic. She has deceived skilled fighters by disguising herself as a child or using transformed victims as bait. During the Battle for Priestella, she demonstrated her ability to predict her opponents’ movements and strike at their weakest points.

Keen Observation: Capella’s observational skills are exceptional. She studies others’ reactions to deduce their preferences, then alters her form and voice to resemble people they admire or despise. She has used this tactic to transform into Emilia and Priscilla Barielle, provoking Subaru and Aldebaran despite never having met either woman.

Little is known about Capella’s past, as her origins and the circumstances surrounding her rise as the Sin Archbishop of Lust remain shrouded in mystery. The author has hinted that Capella is concealing deep emotional trauma from her past.

Nine years before Natsuki Subaru’s summoning, Capella ordered a former slave named Reisel to retrieve an object connected to the legacy of the Witches. The target was a foxlike artificial spirit created by the Witch of Greed roughly four hundred years earlier. To aid him, Capella lent Reisel a magical artifact that allowed limited manipulation of shadows. However, Reisel’s mission ended in failure, forcing him to destroy the artifact. In response, Capella punished him without mercy, transforming him into a shapeless mass of flesh.

At another point, Capella instructed one of her followers, Sithonia, to obtain a perfected curse doll. Sithonia infiltrated the Featherrun sisters under Holosseo Featherrun, posing as a curse doll herself. After Holosseo’s death, she attempted to betray Capella and kill Elsa, but was slain by her “sister.” When Elsa later left the Featherrun mansion, Capella appeared before her, expressing her desire for unconditional love and devotion. By threatening the lives of Ornea Featherrun and Oliver Zeppes, Capella forced Elsa into servitude, making her a new “daughter.” Some time later, Meili Portroute was brought to Capella by Elsa, and the two were paired as her subordinates. It is also implied that Roy Alphard, one of the Sin Archbishops of Gluttony, became one of her “children,” as he refers to her as Mama.

Following these events, Capella continued to issue missions to her subordinates. After Elsa was hired during Arc 1, Capella assigned her and Meili another task, leading to the events of Arc 2. Later, during Arc 4, Meili accompanied Elsa once again despite not being hired by Roswaal, suggesting that Capella was involved in orchestrating the attack on the mansion.