I am not sure about this theory considering that the version we know of Yuuka has existed for a veeeery long time so unless the Dream World jumps back thousands of years I do think this might be a bit flawed.
That or I am just misunderstanding this. I am not discrediting the theory that Yuuka might have been a Fairy in her past. That sounds plausible enough. Just doubt that she became the current Yuuka during Reimu and Marisa's lifetime.
She was a different person at that time. It seems she was more childlike than she is now.Compared to her image back then, they're hardly the same at all, right?Don't you think it means that, at that moment, she became a youkai?As she changed from a fairy to a youkai, so too did her personality and her appearance change as well.If you assume that's true, then there's one thing that's hard to explain.Around the time Kazami Yuuka is showing the students into her homeInside the Hieda home, the two historians are beginning their investigation into that theoryKazami Yuuka was originally a fairyThat theory's pretty farfetched.If you thought she wouldn't come to the temple, why were you researching it?Because that's my role.This kind of thing wasn't written in "Perfect Memento in Strict Sense," right?Now on sale! Very popular!Buy it at regular price, okay?Perfect Memento in Strict SenseBut is Kazami Yuuka such a creature?That's because it's something I concluded from information gathered after it was published.And who is the source of this information?Shikieiki Yamaxanadu-sama.According to her, though rare, it seems a fairy that becomes powerful enough will transcend to a different kind of being.According to Hakurei Reimu and Kirisame Marisa, it seems that, before even the flower incident, they sometimes met Kazami Yuuka in a place called the Dream World.It's belaboring the point, but you can see in her a lot of other fairy like characteristics.FurthermoreIt's quite the interesting theory, but...But what's wrong with thinking that a youkai named Kazami Yuuka lived in the Dream World and then later showed up here?It was only after her encounter with the two girls that she began to show activity in this world.What does it mean?So what's wrong with that?Her appearance changed?Sensei, I don't get this partThe power to manipulate flowers that Kazami Yuuka possesses is similar to the power to control natural phenomena that you often see in fairies, and you could also call her aggressive personality a mischievous one.