Debuting in Arc 5, she acted as one of the main antagonists of that Arc, alongside her fellow Sin Archbishops, leading an assault on the Water Gate City of Pristella. After losing the battle against one of the five Royal Selection Candidates, Sirius was taken into the Kingdom's custody and is currently being held in the Royal Capital's Prison Tower where she remains locked away with the help of Evil Sealing Stones.
Sirius is covered head-to-toe in white bandages, with only her mouth and left eye left unobscured, though some breaches in her bandages allow part of her full head of long silver hair to seep out. Around her neck, she bears a steel choker that has the Witch Cult's coat of arms attached to it. Additionally, something appearing similarly to a red teardrop is constantly affixed directly below her left eye.
Her long golden steel chains are wrapped around her arms and trail along the ground as she moves. These chains have hooks on their edges which allow Sirius to wield them lethally in close combat. Other than her bandages and chains, the only other thing Sirius wears is a long purple cloak. The inside of the cloak is sky blue with several vertical red decorative lines. Although not visible, she carries the Gospel of the Witch Cult around in her cloak.
As shown by her position, Sirius can be wrathful when she becomes angry, though normally she gives off a disgusting aura. She is also Petelgeuse's stalker and is his self proclaimed wife, arbitrarily adopting the madman's surname. She speaks in an intimate, rational manner, but with an off-putting attitude. Sirius has a distinct way of speaking, repeatedly apologizing to everyone about nothing or small things. She does not stand people who belittle her relationship with Petelgeuse as seen when she tried to kill Regulus for that she was disgusting for clinging to a deceased person. Strangely enough, she harbours hatred towards the Witch of Envy, going as far as promising Subaru (who she thought was Petelgeuse) that she would burn her before him if he ever managed to revive the Witch. Sirius despises any woman that's too close to her beloved Petelgeuse, as seen when she expressed her hatred towards Beatrice for simply standing next to Subaru (who Sirius thought was Petelgeuse) and asking him what he found so appealing about her, before threatening to burn her alive.
Sirius demonstrated a twisted and freakish view on love. In her opinion, the best representation of love is to become one. To her, love is a prayer for becoming one. Seeing the same things, feeling the same emotions, living the same life, ending the same death.
Currently, little is actually known about Sirius' past including how she became the Sin Archbishop of Wrath and how she obtained the Witch Factor of Wrath. However, according to her, her hometown was destroyed by a Witch Hunt long ago although nothing else was said about that incident. Presumably, since Sirius's Authority grants her extreme longevity, she has lived for a very long time, though it is unknown how long.
Some time after the events of Arc 3 and her beloved's death, Sirius managed to collect his remains and take them to an unspecified location where she set up an altar. After being subjected to Greed's wrath through the Conversation Mirrors and ripping off her nails, she cremated Petelgeuse's remains, promising the two will meet again.
Around that time, Sirius tracked down Petelgeuse's surviving fingers, ripping them apart in search of her beloved.
Authority of Wrath (憤怒の権能 Fundo no Ken'nō): Sirius is able to use the Authority of Wrath.
- Wrath (憤怒 Fundo): In a large but currently-unspecified area of influence, Sirius can share or transmit her emotions and senses to others. After polarizing emotions such as anger, sorrow, joy or ecstasy, she can transmit it to any person in her vicinity, either taking control of them or resonating a certain emotion between a certain amount of people to raise it to the point of madness. Also, since she can share senses such as distress or pain, if anyone is injured or dies within the area of effect, she can force others within the same area to die or receive the same injuries, in the same way. The Authority's intensity seems to fade the further the range and extension, and the effectiveness can vary drastically between people.
- Longevity: Sirius possesses an abnormally long lifespan presumably due to her Authority of Wrath, though the specifics behind her longevity have yet to be revealed.
Inhuman Strength: She is said to have the highest physical strength among the Archbishops. Sirius can easily withstand strong attacks by simply blocking them with her bare hands. During her confrontation with Reinhard in the 3rd failed loop of Arc 5, Sirius displayed inhuman strength and resilience by blocking one of his kicks, which are power enough to send Steel Humans flying.
Magic User (魔法使い Maho Tsukai): Sirius is a master of Fire Magic, though her application of the Fire element is a bit different than most others'.
- Chain Control (鎖操作 Kusari Sōsa): Sirius wields long golden chains made out of solid-metal with razor-sharp hooks at the ends, which she tends to wrap around her entire body. The length of the chains seems to be infinite, and she stores them away in her black coat's sleeves or materializes them from thin air. When entering combat, Sirius shoots them out, and freely controls their path of flight – it was mentioned that her control over her golden chains was unnatural and superhuman, as she could seemingly-telepathically change their trajectory mid air and home them on her target. The chains are incredibly sturdy and powerful, being capable of easily shattering stone walls with a single strike. Combined with her superhuman strength, incredibly mastery of Fire Magic and her ruthlessness, Sirius is easily able to overpower even the strongest of foes by repeatedly slashing at them with her golden chains with such force, that the sky was described to be just about ready to split in half. Furthermore, Sirius can also use her chains to propel herself to higher places, as was shown seconds before she was cut down by Reinhard in one of the failed loops; by extending her arms wide, she shot out her golden chains and hooked them to nearby buildings, launching herself up in the sky. Lastly, it should be worth mentioning that when serious, Sirius clads her golden chains in fire which burns so hot that it can easily shatter Emilia's Ice spells which can resist even the highest of heats.
- Fire Control (炎操作 Honō Sōsa): Sirius exhibits an uncanny mastery of Fire Magic, being capable of easily enveloping her arms or objects in scorching-hot fire that can melt even Emilia's sturdy ice. By simply holding an object in her hands, Sirius can clad it in flames and greatly amplify her damage output. Having said that, the most common application of this technique can be seen with Sirius' golden chains; by wrapping them around her arms and igniting them, Sirius effectively turns her hands into flaming swords which can easily deflect sword or spear attacks, and deal massive amounts of damage. Additionally, Sirius can preform ranged attacks using her Fire Magic; by enveloping her chains in fire, she can hit distant opponents not just with strikes capable of severing a human being in half, but she can also scorch them to death. During her confrontation with Regulus in Arc 5, Sirius managed to envelop Regulus in a vortex of apocalyptic flames that rose above the giant Time Tower and even melted the stone tiles on which Regulus was standing. Mere minutes later, Sirius proceeded to split the earth between Subaru and Regulus open and create a sea of flames between the fighting duo. Her Fire Control has been described as supernatural.
- Witch Cult's Gospel (魔女教徒の福音): As a member of the Witch Cult, Sirius is the owner of a copy of the Witch Cult's Gospel. Each Witch Cult Gospel is a replica of the Book of Wisdom, a book that had been in the possession of the Witch of Greed Echidna. The Book of Wisdom would provide exact details of future events concerning the Witch of Greed, essentially bestowing Echidna with a form of precognition. Unlike the original Book of Wisdom, the Gospels of the Witch Cult are imperfect replicas, meaning that, although they detail the future of its owner, the events conveyed are subject to change and the information provided is often up for interpretation. The Gospels take the form of small black books that can only be read by their owners.
- Sirius' name comes from the star Sirius, which is part of the Canis Major constellation and also the brightest star in the Earth's night sky. Due to Sirius being the brightest star, it is commonly called "The Scorcher", which also references her usage of Fire Magic.
- She possesses abnormally bad luck. On the way back to the capital, the dragon carriage transporting Sirius was attacked by numerous bandits, was exposed to many rare inconveniences, and was even forced to take a detour due to a sudden Demon Beast migration.
- Despite her journey to the capital lasting roughly a month with many misfortunes happening on the way, no member of the Witch Cult came to rescue Sirius.
- "Sirius exhibited incredible skill as she freely manipulated the flight path of her chains in midair. There was no mistaking that Sirius' mastery was beyond the ability of any ordinary human." Re:Zero Light Novel Volume 17 Chapter 1; Section 6