After discovering that she had been "replaced by a doll," Louisiana discarded the name of Valliere and chose to adopt her current name. With her Familiar's help, she revived the name of the Phantomhive Nobles, quickly proving her legitimacy as a blood relative of the house and becoming the rightful heir.
Louisiana is one of the few living Void Mages in the entire world, becoming the unofficial fifth Void Mage. Additionally, she is the master of the demonic Familiar, Sebastian Michaelis. Unlike most contracts, Louisiana has sold her soul to him. Once the contract ends, she will die.
When introduced for the first time, Louisiana displays a cold front that is enough to leave even someone as boisterous as Osmond on edge. No-nonsense and stoic, she chooses to cut straight to the heart of the matter rather than beat around the bush. She quickly lives up to her reputation as the Black Mage, for when faced with someone she dislikes or holds no patience nor tolerance for, she will not hesitate to verbally abuse them in a calm and calculated manner in order for them to retaliate.
Amongst most Mages, Louisiana is cunning, planning things ahead of time and keeping in mind possible variables. She describes herself as a "retentive tactician who is a sore loser," implying that when things don't go the way she plans them, she is most certainly not happy. This fact is further supported by Sebastian, who once mentioned how Louisiana threw a tantrum when she couldn't defeat him in chess despite accurately figuring out his moves.
As Osmond is quick to notice, she holds a deep hatred for nobility who cares nothing for others, not even their fellow noblemen. Her ire is especially directed at the House of Valliere, who she describes as "arrogant fools and cruel monsters worse than elves." Her opinion of them is harsh and critical, though this stems from discovering how she was "replaced." Even when Duke Valliere explains the truth to her, she still holds nothing but contempt for them. If anything, discovering the truth has only increased her hate for the Valliere family. The only members barred from her wrath are Cattleya and Louise.
In their first meeting, Louisiana shows nothing but open hostility and loathing towards Louise, calling her a "fake," much to her initial confusion. However, the hostility is soon reciprocated when Louisiana mocks the Valliere Family before her, thus solidifying the two's hate towards one another. After discovering the truth regarding herself and Louise, however, she shows regret for belitting her sister like that, remarking that she was just as much a victim of her family's horrible nature as she was. Since then, she has tried to make amends while also slowly convincing her of their family's hypocrisy.
In spite of her negative aspects, she is not without positive ones. Unlike most nobles, Louisiana cares for the commoners and Servants who work under her. She praises Guiche's uncanny "valkyrie" scuplting abilities alongside Kirche's impressive control over fire magic. She also finds common ground with Matildo, as both women can relate to their pain caused by others. She also treats Siesta respectfully, even teaching her subjects privy to the nobility. In spite of her awareness that she will one day die once their contract has ended, Louisiana holds nothing but respect, if not outright admiration and love, for Sebastian. That said, however, both have stated that they are merely using one another for their own ends, making their true relationship ambiguous.
Louisiana was one of the two youngest daughters of the Valliere Family. Originally named Louise alongside her twin sister, they shared a near identical life together, yet for some reason they never had any memory of one another whatsoever.
At some point in time, Louisiana's fate becomes similar to that of Ciel Phantomhive from Black Butler, having been taken from her home and tortured. At some point, she entered into a contract with a demon, who she named Sebastian Michaelis (the name of the butlers who died trying to protect her). Soon after she escaped, Louise was ecstatic at the prospect of returning home...only to discover a girl exactly like her to be living the life she was supposed to have.
Upon investigation, Louisiana learned that the girl was "Louise Francoise le Blanc de la Valliere," the youngest daughter of the Valliere Family. As it turned out, the two were identical twins who shared the same life. The only reason neither of them remembered anything about the other was because their parents made it that way. To Louisiana, it was no better than a betrayal. In the future, she would consider this to be the day when she discovered the Valliere Family's hypocrisy and swore an oath to bring an end to the wretched family legacy.
To this end, Louisiana forsook her original name, claiming that if a doll had taken her place, she would become someone else - someone who would bring nothing but misery to the name of Valliere. Remembering that her mother once told her that she was related to one of the most powerful noble families in all of Halkagenia, she ordered Sebastian to look into the matter at once. Shortly after, the two went about restoring the fallen noble house to its former glory.
Thanks to Sebastian creating false, yet truthful documents, Louisiana was recognized as the only living heir to the forgotten name of Phantomhive. From there on, she became known as Louisiana von Phantomhive, and soon made good on her promise by becoming known throughout the country as the "Black Mage" - a noble powerful enough to end another's life with but a single spell, and known for her cold heart.
As the Heir of Phantomhive, Louisiana was also granted the title of "Queen's Guard Dog." With this position, Louisiana was to handle any and all cases that could not normally dealt with via ordinary means.
Compared to her canonical counterpart, who discovered the true potential of her "failed magic prowess," Louisiana has quickly mastered the power of Explosion to the point where she can control the size of the blast radius, as well as the power behind the blast. On more than one occasion has she killed a noble in a single cast, obliterated several enemy soldiers, and even felled a dragon.
- It is never stated, but implied that Louisiana's Phantomhive relative was the Ciel Phantomhive of the Zero no Tsukaima universe. According to Henrietta, the dark noble was very young and died while he was still in his twenties, and was known for his cold methodology and tactics, earning both recognition and scorn from all sorts of places.
- Louisiana's backstory is similar to Ciel Phantomhive's apparent history, as it was revealed that he had a twin brother, and that he was apparently a "spare" for the heir of the Phantomhive.
- Similar to Ciel, Louisiana's contract stigmata is located on her eye, covered by an eyepatch.