Cecilius

Cecilius Fofilius is a cryptic and strange girl, it doesn't help that her elder brother was expelled from Hogwarts shortly before she arrived at school. Shortly after his expulsion, Jace disappeared from home. Their parents were strict and forced their children to study rigorously. At first, Ceci kind of assumed Jacilius ran away because he hated their parents, but when she stole his letter from Hogwarts notifying her parents of his expulsion, she learned he was searching for the fabled Cursed Vaults in the school. Since then, Ceci has become obsessed with uncovering the truth of the Vaults for herself. 

Many students (and teachers) spread rumors and she isn't very liked, her reputation was already soured by her weird elder brother, and the only teacher who treats her normally is Snape; because he treats everyone terribly. She ignores the whispers and keeps her mind occupied with classes and finding Jace. Almost immediately she was confronted by another student by the name of Merula Snyde, who has apparently made it her goal in life to torment Cecilius and her friends at every opportunity. Through her exploits over the school years, quite a few people flock to Ceci (although far more choose to avoid her) and become her friends. At home, her family rarely showed emotion, it was so different to be surrounded by people smiling and laughing. Though Ceci was a glum recluse, she can't help but smile at their dumb jokes (Tulip and Tonks have even convinced her to pull a few pranks on occasion).

Sometime during their third year, Cecilius overheard that a mysterious student was attempting to brew an Animagus potion, which was said to be very difficult to do. Ceci decided to seek them out, and offered the student (whose name was Talbott Winger) some help. They said they already had a friend helping with the potion,  but wouldn't turn down further assistance. After gathering some ingredients needed, Ceci was surprised to find out Talbott's friend was Penny, her own best friend. Throughout the tedious brewing process, Ceci learns the elusive Talbott was harboring a secret; he himself was an unregistered Animagus. He asks her to keep it quiet and she agrees. Upon completing the potion Ceci consumes it and successfully becomes an Animagi.

After opening multiple cursed vaults and getting closer to solving the mystery, Ceci aids her friends in preparing the Celestial Ball during year 4. Whilst decorating away, her friends begin to question who exactly she's bringing to the Ball. This isn't something she's really thought about, and when confronted with the idea of dating somebody she thinks of Merula. During the days leading up to the Ball, Ceci works up the courage to ask her out. Through some miracle, Merula says yes, and they actually have a pretty good time together at the dance. 

A short time after the dance, Penny approaches Cecilius because she is concerned about Talbott. Apparently he has been missing classes and acting even more reclusive than usual. Cecilius hasn't talked to him since she became an Animagus in fact. It's not that she didn't want to per se, he was just never around. Nonetheless, she agrees to help so Penny won't have to feel distressed over it. She decides to ask Professor Mcgonagall about it, since she's Talbott's favorite teacher and they have a good relationship. The Professor says Talbott mentioned losing his necklace, but was acting strange even before he lost the item. Ceci approaches Talbott in the courtyard and asks him about the necklace, and he admits to losing it. She offers to help him search and he reluctantly agrees, so the two go off searching every corner of the school. While searching, Cecilius starts to learn more and more about Talbott's life, and she begins to piece together why he's been acting so off. After extensive searching, they manage to locate it and Ceci retrieves it by using her cat form. He thanks her greatly for her help, since the necklace is the last remnant he has of his mother. It turns out his parents were killed by Death Eaters, and its hard around this time of year as it's the anniversary of the tragic event. Losing the necklace just plunged Talbott into an even worse state, it felt as though he was losing them all over again. He says he doesn't enjoy being around other people, but somehow Cecilius is different, and now he considers her a trusted friend. After this, he still keeps to himself, but on some lunches he asks Cecilius to come away from her loud friends and sit by him, which she happily agrees to (her friends can be a bit tiring sometimes) and the two enjoy quiet conversation.