세상이 다 등 돌리더라도 난 네 편이야

The line, explained

At level three you have met -아/어도 a hundred times: 괜찮아도, 바빠도, 늦어도. Today's line uses its heavier cousin, -더라도, and the choice is not random. -아/어도 concedes something plausible. -더라도 concedes something you are willing to picture at its most extreme, and then plants a flag anyway. That is why it belongs in a chorus about loyalty: the singer is not saying 'if things get a bit rough'. They are saying 'even in the worst version of this'.

Walk through the words. 세상이 is 세상, 'the world', with the subject marker 이. 다 is the little adverb meaning 'all, entirely', and placed before the verb it scales the picture up: not some people, the whole world. 등 돌리더라도 carries the idiom. 등 is your back, the part between the shoulders, and 돌리다 is 'to turn (something)'. 등을 돌리다, 'to turn one's back', means to abandon or reject someone, just as in English. Lyrics often drop the object marker 을, so you get 등 돌리다.

Attach -더라도 to the stem 돌리- and you get 돌리더라도, 'even if (it) turns'. The form is friendly: no 으 to insert, no vowel to match, it sits on any stem as is. Historically it is -더- (the retrospective marker you know from -더라) plus -라도 ('even if it be'), so it literally says 'even if it were observed to be so'. You do not need the etymology to use it, but it explains the slightly formal, resolute colour it adds.

Then the turn. 난 is 나 with the topic marker 는, and here the topic marker is doing its contrast job: the world does one thing, 난, I, do another. 네 편이야 is 네 (your, from 너의) plus 편, 'side' in the sense of a team or faction, plus the casual copula 이야. 네 편이야 is a phrase Koreans actually say to each other, in hospital corridors and group chats: 'I'm on your side'. Hear a parent say it in a drama and the subtitle will usually read 'I've got your back'.

Try the substitutions and listen for what survives. 세상이 다 널 잊더라도 (even if the whole world forgets you), 세상이 다 무너지더라도 (even if the whole world collapses). The second half does not budge, which is the point of -더라도: it sets up a condition precisely so the main clause can refuse to depend on it. If you want the colloquial version for texting a friend, 세상이 다 등 돌려도 works fine. Save -더라도 for when you want it to sound like a vow.