Quote Originally Posted by Buffalobiian
The song was originally composed as a farewell present for Sana all those years ago. Now, after the time skip, it's finally been completed, but this time with the experience that they've all been through, ie the anime. Since the song represents all they've been through, the anime's title: Myself ; Yourself.
That's it.
Their full story, including their will to suicide themselves at some point.