Well, about the plot device thing...here's Vinno's backstory if its any help, none of it is IC knowledge but I feel it explains the way she acts, I'll let you guys handle that.
(It's okay if you don't want to read it)
[spoili]
First of all her parents are actually more developed characters than she is...so that's that, most of this would be about her parents. Her parents were a pretty prime example of why society should treat mentally unstable people well, her mother Mina Cres was a shell-shocked war orphan who mastered the magic of manipulating emotions to hide from her own trauma, and her father Akia Sion Helinens came from a prestigious family that ran a big guild. He was a really sickly kid (that's why Vinno is sick all the time) who can't fight back when his father and older siblings stole his research thesis.
They were both Tower University students, or drop outs to be exact because Akia tried to commit suicide but was stopped by Mina. Then they both dropped out of school, Akia got disowned so his name is just Akia Sion now, and tried to commit every white collar crime in existence. So they went to do some not blatantly illegal but still taboo studies. Mina does the emotion thing because human impulse and negative emotion is what caused her life to be ruined, and Akia tries to find a way to erase human desire because his family's desire to use him for fame and gain is what caused his life of misery.
In the end they did succeed and became quasi neuroscience experts/mathematicians (Why Vinno only takes numerology and talks about geometry with casting circles all the time). For most of their time after that they run an angecy called the "Soul Surgery Department" where they use illegal magic to completely alter people's personalities on request. It's kind of an illegal business similar to drug trafficking I guess. Vinno was born as some sort of contract between the two, and since they were both borderline psychopaths at this point she never realized they were her parents until later. She called both of them by first name and never had a last name from either of them. (But if she did it'll be "Cresion", yes, I remember that rule) She was also used as a sort of experimental subject for micro-changes, and her personality, desires and emotion levels were artificially changed a few times during her childhood. This kind of resulted her unable to emphasize with others too well. (mainly shown in interactions with Wolfgang and Yumi). Other parts of her childhood were just learning the basics of magic, becoming really advanced in math (because having a math genius in a magical world is fun, I guess) and also understanding some of the mind manipulation spells her parents use.
So the illegal surgery business was fine until her parents was founded out by other black magic users who was part of some organization (well, cult, if we did established that) who started to threaten their lives to get their research on soul manipulation. Her parents pull their last resort, which is a spell that eliminates a person's mental state completely, their desire to move, eat, sleep, socialize s gone as well as their will to live, and emotional connections with other people. This made them basically first degree murders instead of just underground dealers, the cult's more "clean" members framed them for murder, her father is in maximum security and her mother was witnessed to commit suicide, but her remains were never found. Vinno was adopted by her father's distant relatives. (Hence the surname, Linens is just the last part of Helinens) Her family's connections with the cult was never known by anyone, it was treated as a murder case and she 8 years old at the time, after that she laid low so no one really knows her. [/spoili]
