She has always worn the tie from the male uniform. It doesn't represent any kind of transition, it's who she has always been. Also, having "masculine" fashion choices does not make somebody genderfluid or mean they have a masculine identity. SJ has always expressed herself as female, and being a female who likes more boyish fashion is just as valid an identity as anything else.
Ah yeah I get it. But what I don't understand is, her school does have rules and I'm confused because Sun Jing wear it like it's normal, when it should be for male students. Like, I don't know if it's allowed tho.
Many schools have different levels of strictness on the uniform code. Probably for her school students are required to wear either the ribbon or tie, but the code is nonspecific as to gender. Sun Jing clearly likes to stand out, so she wears the tie because it's a way in which she is allowed to be a little bit different from the other girls. IOW, She's probably exploiting a loophole in the uniform code as a way of expressing some personality.
I just noticed this-
Why the heck Sun Jing wore male's tie?!