Like, I know there's all that talk about Rin being ugly in Nikan, and she even says that about herself, but I don't think so, and I can argue against it.
This whole story about Rin being ugly seems very racist/imperialistic to me, since Nikan hates the Speerly and doesn't even consider them human. Besides, they have dark skin, and the Nikan value fair, immaculate skin like porcelain. But when Altan was in Sinegard, everyone adored him and considered him very handsome, even though they were wary of him because he came from Speer.
And there's the way the Nikara people of the north treat those from the south, so it's clear that by that country's beauty standards and Rin's social class, she would be seen as ugly. However, there are some nuances to this. Because, even though Nezha teased her and said terrible things about her and her skin color, he never explicitly used the word "ugly" to refer to her, and later, Nezha admits that Rin is the most divine thing he has ever seen in his life. Yes, it has to do with their relationship with the Dragon and the Phoenix, but the Dragon doesn't tolerate ugliness; he feels repulsed by ugly people, so it doesn't make sense for Rin to be something divine to Nezha if she wasn't beautiful or attractive enough to the Dragon.
Even though it's implied and you have to read between the lines in the book, Rin is the daughter of Jiang and Hanelai, with Hanelai being Altan's aunt, making Rin his cousin. Jiang is described as handsome, even possessing a timeless beauty. I believe Hanelai is beautiful too, even though Jiang probably values things beyond beauty; at the end of the day, he's a nikara man, so it could be said that he was attracted to Hanelai's beauty. Besides, Altan was incredibly handsome. Do you agree with me that having two supposedly beautiful parents would mean they would conceive a beautiful child as well?
There are many factors we can discuss regarding Rin's beauty, mainly concerning the social/ethnic class she belongs to. No one has ever seen the offspring of a relationship between a Nikara and a Speerly, so it was obvious that Rin would be viewed with suspicion. And she hasn't had access to learning about how to take care of her appearance (and I think she doesn't care either), so it was obvious that at first glance she would appear inferior. And there's the fact that nobody said Rin was ugly throughout the entire trilogy (that I remember), they only stated the obvious: she could be considered ugly because she didn't meet Nikan's beauty standards. But we, as a society, know that not being the standard doesn't always automatically mean a person is ugly.
So, for me, Fang Runin must be beautiful, and I stand by that view. If she had grown up with her mother or had someone who cared about/encouraged Rin to take care of her appearance, she would indeed be considered an exotic beauty (which is a very racist term, but it would fit here). I don't believe Rin is ugly at all; I think Nikara society is prejudiced, and Rin was close to the elite, so she wouldn't be viewed favorably.