"Postscript" is a Life is Strange-inspired indie-folk song written and performed by Koethe, which addresses the "Sacrifice Arcadia Bay ending". It was released on December 30, 2015.
Koethe explained on Tumblr that this song is about Max not being able or willing to let go of Chloe, and sort of having to come to terms with the fact that her choice may not be the “kind” or “moral” choice, but what is right for her even if she feels bad about it. Similarly, it's saying that of the two of them, Chloe is more selfless when it comes down to situations like this one, since she is willing to sacrifice literally everything including herself to save other people, whereas Max is willing to let others' well-being be left to fate in order to save Chloe.