Sistine Fibel (システィーナ • フィーベル, Shisutīna Fīberu) is the Tsundere character in the Rokudenashi Majutsu Koushi to Akashic Records (ロクでなし魔術講師と禁忌教典 Roku de Nashi Majutsu Kōshi to Akashikku Rekōdo) series (also known as Rokuaka).
Sistine has thick, flowing and somewhat straight silver hair (lavender hair in the manga) with a small ahogehair-line. Her hair is mostly worn down and accessorized with a blue-and-white headband with a pair of cat ears attached to it. She has olive green eyes. Her nickname “White Cat” was given by Glenn Radars, which stemmed from her cat-ear headband, much to her annoyance. She mostly wears the Alzano Academy uniform with or without the raiment depending on the seasonal weather.
Sistine maintains a hostile and no-nonsense demeanor and often scolds Glenn Radars due to his lackadaisical attitude; she was at her meanest in Episode 1, when Lynn Titis asked Glenn a question, and when he (Glenn) didn't answer, Sistine had to angrily confront him, causing Rumia Tingel to calm her down.
Sistine has the personality of a modern Tsundere character, and switches between nice, kind, and supportive, to hostile and mean towards Glenn, but eventually got rid of her aloof personality when she came to accept what a good teacher Glenn was. Despite the fact that Glenn is a teacher, Sistine doesn't hesitate at all to scold him or even talk down to him, even using violence and insults when she gets flustered or annoyed by his actions.
Sistine has a contrasting personality with Rumia. While Rumia may seem weak, she is actually strong and knows how to stand her ground. On the other hand, Sistine tries to put up a hostile and tough front but this is just to hide her weakness.
Sistine tends to act snobbish and boastful at times due to her aristocratic background. She is also quick to defend those she cares about and can be very mouthy.
Sistine is low-tempered and hot-headed as shown in Episode 2, where Glenn then explained to the class that he was able to influence Sistine's mind through the use of words, and then she threw her textbook at Glenn, and then when Glenn replied, she threw a terrible tantrum. She is also rather hard-headed in pursuing the path of magic, relentlessly inquiring about points she did not understand during lectures, to the point that she became known across the school as "Sistine the Bane of Teachers" (講師泣かせのシスティーナ, Kōshi Nakase no Shisutīna).
While not a welcome nickname, she finds pride in it as proof of her uncompromising and earnest efforts. As the head of her class, she tries to keep her classmates in high spirits and is very supportive of them.
She has confronted Glenn frequently throughout the series, and she was at her meanest towards him in Episode 1, where she got angry at him several times, challenged him to a student-professor duel (during the duel, she frequently, intentionally, and angrily performed Shock Bolton him to show that she is much better than him), took off her glove and threw it in his face. In other episodes, Sistine threw tantrums and got mad at Glenn, and even slapped him in the face, and told him that she hated him, running away crying after that. She initially hated Glenn Radarsbefore eventually accepting what a good teacher he was.