so i want to preface this by saying that while i am taking the time and patient to explain this, i do feel that an expression of anger and frustration is a perfectly valid reaction at all and i would not like for my reply to be used as an example for how people "should" react to things like this. i am writing this as someone who is east-asian and southeast-asian, and it relates directly to my experiences with representation in media and rp.
first of all, when writing an east-asian character as a non-east-asian person ask yourself why it is that you feel compelled to write and east-asian character. what is the story that you want to tell? why is it that this story cannot be told by a white character, a brown character, a black character etc. etc. keep in mind that you are writing this character on a site where east-asian people will have to experience your interpretation of an east-asian person. yes this is rp, but even in rp your actions affect real people. if you still feel like you want to write this east-asian character and that you can do a respectful job of writing this east-asian character (without being fetishy, stereotypical or dismissive) then this is a good sign that you're probably ready to write an east-asian character as a non-east-asian-person.
when you choose a pb, i think it's important to be aware of the long and painful history of erasure of east-asian/southeast-asian characters and identities in western media. it's a problem that prevails and sustains damaging attitudes towards ea/sea people. chinese and korean cultures are vastly different, there are long histories and political and cultural strain between the two countries. we understand that in hollywood, an actor must do what they must in order to get the role. most people can name on one hand, the number of east-asian actors in western media. in rp, your possibilities are endless. you can pull east-asian faces from all over the globe and stick then into any setting. in my opinion, there is no reason that you should be playing a chinese person with a korean face. to me that reads like you don't care that their cultures are different, that they really don't have anything to do with each other other than proximity of their countries. that is the root of why things like this are racist.
i hope that this makes sense, i can feel myself rambling towards the end there. feel free to ask, if you still have questions and i will do my best to answer them. and to re-iterate again, please respect that not everyone will have the resources (mentally, and otherwise) to give a kind or patient response.