Tangent, but it actually happened, and I'm doing my best to recollect the conversation:
I once met a young lady for coffee. (It wasn't quite a date, but a situation which could eventually lead to being retconned as a date.) She asked me, in a fashion which struck me as out-of-the-blue, "Do I strike you as a typical Japanese girl?"
I figured that she was fishing for a compliment (thought process: "Who would want to be as-sent-by-central-casting?") , so I said "Oh no, you strike me as different."
She immediately burst out crying, and asked "How did you know?"
"I'm sorry I'm sorry I'm sorry. I didn't mean it to be taken that way. I thought you wanted me to say that you were a unique person."
"No no I want nothing other than to be a typical Japanese girl."
"What does that... OH GOD. I'm sorry I'm sorry I'm sorry no it is absolutely not possible that anybody could guess that you're ethnically Korean." (The word in Japanese is "zainichi", for 在日韓国人, the literal translation of which is "A Korean who lives in Japan.")
"... Wait you know about us?"
"I studied a variety of esoteric things in college."
"So you don't think less of me for being... you know..."
"NO NO NO NO."
Cue about an hour of talking about it. She said that none of her friends knew. I said that 2007 was a very different time than e.g. 1970 and they'd probably be understanding. "Maybe, but I can't unring that bell. What if one of them hates Koreans? What if all of them hate Koreans? What if I told? I'd never get my life back."
Tangent over.
Do you believe a piece of paper which says "My grandfather is named Kim" fails to have a consequential effect on this young lady?
(Controversial opinion for Japan incoming: She's Japanese, not Korean, under all the laws of earth and heaven. She was born in Japan, she speaks no language but Japanese, she carries a Japanese passport, she carries no other passport nor desires one, she is entirely culturally Japanese, she feels no feelings of belonging to Korea, actual Koreans would not treat her as being Korean, etc etc ad nauseum, but there exists a not-tiny contingent of her fellow countrymen who would immediately fire-in-the-eyes hate her if they somehow came to believe she was Korean.)