Here it is: the OST from Nagi-Asa: A Lull in the Sea!
Rather than link the whole OST right away, I'm going to link a few of my favorite songs.
1. Two-Sided Feeling
3. The Heart That Slips Through
This is the full OST, parts 1 & 2 both. Enjoy them!! It's over 2 hours of music in all, and it's all beautiful to listen to. The nice thing about listening it to it all together is because the songs blend so well together that you really don't feel like you're listening to a bunch of songs, rather, to a long work that flows together really well.