
On Chapter 63 when Aoi changed into a human form the kimono worn was a woman's style. So, I had been thinking is Aoi-san a female?
Chapter 64 basically confirms it haha! Aoi-san is indeed a female.

Not necessarily. Aoi is a unisex name used for both men and women, not to mention in the raws, Aoi has been referred to in gender-neutral terms. Aoi is capable of turning into many forms, which means they could easily take the form of an animal, a man, or a woman if they so wished.
What I'm trying to say is that while it is possible that Aoi is a woman, there is also always the possibility that Aoi is a long-haired man who finds women's style kimono comfortable and enjoys dressing in them.
It's also possible that Aoi just prefers appearing in a female form when they aren't in the cat one, and it has no real bearing on what they actually are.
I don't think we can really know for sure until we have more information about Aoi, which so far we haven't gotten much of, I think some more waiting is in order before we can really say for sure.
Aoi could very well end up being trans, genderfluid or non-binary in the end for all we know.

I didn't mind the girl at first but the new chapter is worrying. I thought she genuinely wanted to support the relationship between the two. But, it seems more as if she just wants her fantasy like assumptions about gay relationships she reads on mangas to come true.
Reality isn't so pretty. I feel a misunderstanding might sprout between the two thanks to the girl's naivety.
Looking forward to he nxt chaps~

Does anyone by chance know if this manwha is based on a novel?

It is, but it isn't translated. Some of the other names for it is Queen with a Scalpel and Surgeon Elise. The Korean name for it is 외과의사 엘리제 if you want to try to find it...
https://forum.novelupdates.com/threads/does-the-manhua-queen-with-a-scalpel-have-a-novel.71132/
I got an update notice on this and I was absolutely elated!! Only for it to be a false alarm?!?! Whyyyy youuu do thiis too mee??!! (╯°Д °)╯╧╧
My heart is fragile enough as it is!!
XD
XD