내 이름 석자 그 가장 앞에 와야 할 But
‘But,’ the word that should come before the three syllables of my name
Note: I’ve seen many people speculating that he is aware of and is using the “but Namjoon- ” thing. I personally strongly doubt if that’s the case since (1) it is almost strictly used in non-Korean (language-wise) fandoms, especially on “stan Twitter,” and (2) it doesn’t really work within the context anyway.
My interpretation of this line (again, this is my personal interpretation) is that this really is about his fundamental question, the question he’s been asking himself for his entire life and is still trying to figure out the answer (if there is one) for, the question that pops up every time he agonizes and regrets, and the question that really penetrates through the entire song. “But, who am I?” “But, (who is) Kim Namjoon?”
https://doolsetbangtan.wordpress.com/2019/03/31/persona/