Oh, wow! That was absolutely beautiful! In fact, I might just listen to it for the 263376423546th time once I finish writing this reply.
I'm guessing that this is a remastered version of one of the songs that was on the Sega CD version but was removed in the remakes. Well, just hearing this beautiful piece makes me want the original games even more. <3
5:07 into the video is where the song is from. It's sort of the theme song for Luna and Alex. It plays a few times throughout the game and it's the song they sing/play at the Burg Springs back when Alex used a harp. Glad you like it, Klover.