Hi,
In the very last episode, K says goodbye to everyone and to Stephen. The episode ends with her (in a tank top, hair tied up) leaning onto the fence, facing the sea and that's when the songs comes on for a few minutes, until the entire season wraps up...
It's a female voice, a relatively slow song. Once again, at the very end of the last episode.
Thanks a ton if you know this song! It is absolutely beautiful!