So after seeing the trailer I'm confused which one is the main lead cuz they both have strong chemistry with the…
In the novel really both, because in the book the true love of Xiao Su is Zen Rong but she discovers that Yu Zheng is not only the older brother of Zen Rong but also the guy who took her virginity (it was a one night stand) and the only guy she's ever slept with. This discovery becomes an obstacle in her relationship with Zen Rong. Also Zen Rong will die and Yu Zheng will then play both the role of her tormentor and guardian angel until he rapes her and she becomes pregnant. She will then only have hate for him. Yu Zheng will eventually understand that he's fallen in love with her long ago but it's unfortunately too late because it's after the rape. I don't think the drama will have the exact same plot as the novel though because chinese dramas usually aren't really dark or at least i've never seen one and the novel truly was. In fact, it was one of the saddest and darkest book i had ever read and tho Yu Zheng does a lot of other unforgivable sh*t i didn't mention above, it was also because the writing style of the author was sooo good like u literally felt like u were the characters and i swear to god i was depressed for a least the whole day and i would've cried (and i never cried for a book before) if it wasn't for the fact that my brother was with me at the time.
Why is her nationality is American? Is she half Or what?
Her ethnicity is completely Chinese (both her parents are Chinese) but she holds the American citizenship, meaning she has all the rights of an American person (ex. : vote for the political party she wants). For exemple, you could be a full Japanese ethnically but still have a French nationality because one or both or your parents (if you are a minor) or yourself (if you are major) changed your nationality from Japanese to French