Intellect
Sayori Wakaba was not an idiot.
As a matter of fact Sayori Wakaba could probably be called the very opposite. She had both book smarts and street smarts, and a naturally inquisitive mind. She'd gained many friends in her short life and knew how to use these friendships to mutual advantage. This is not to mention the natural empathy she possessed (and utilized to its full potential)
Yes, Sayori was a smart girl. Smart enough to know something was not right with her closest friend… Yuuki Cross.
Yuuki had always been a little bit different from the other girls at school; this had nothing to do with the fact that her father was the school chairman (though it probably didn't help). The truth of the matter is that Yuuki was simply very strange. Sayori knew that, she realized it from the moment she first spoke to Yuuki.
The girl exuded an overwhelming happiness which would be considered unnatural if coming from any other human being. Upon their meeting Yuuki had exclaimed that "Wakaba Sayori-san" was simply not a fitting title for her newest best friend… she was "Yori-chan" from that moment on. This sort of candid friendliness had, in time, become characteristic of Yuuki's personality… So it shouldn't be considered strange that when Yuuki stopped sharing her stories with Sayori, the later became worried.
For many months now Yuuki had been becoming distant, their weekly voyages to the world outside of Cross Academy had become less and less frequent, to the point that Sayori didn't bother preparing anymore, knowing full well what she'd be waiting outside of the school gates for hours, only to walk back to her dorm after dusk, Yuuki still no where to be seen.
The prefect never gave an explanation for her tardiness, and truth be told Sayori didn't want one. God only knows what was keeping Yuuki on the other side of school until dawn. And frankly, she was afraid to ask why her friend was almost constantly to be found with bandages wrapped tightly around her neck.
However, regardless of how little she wished to understand about the situation, some baser instinct told she had to make sense of the situation.
The poor girl spent agonising hours in a futile attempt to put all the puzzle pieces together, but nothing seemed to make fit. At one point, for the most fleeting of moments, Sayori had almost convinced herself that the Night Class was made entirely of vampires, and that the prefect duties Yuuki had adopted at the start of the school year (the very duties which had sparked the rift between Yuuki and herself) were actually a cover, so that she had Zero Kiryu could patrol the school at night and keep the human's safe.
But of course this theory was quickly thrown aside. The very idea of vampire's was idiotic… and Sayori Wakaba was not an idiot.
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Author's note: there is my first Vampire knight Fan Fic. I'm actually feeling rather proud of myself. There are definitely a few things I could fix, but for now I'm happy with it.
Why Yori-chan you may ask?… who better I answer :