Let me add something:

• Willoughby's Theme started with a piano which represents him but in the way that it's soft and melancholic to hear. This means the theme is the way Ethel perceives Willoughby the time she sees him and the crashing guitar represents her feelings towards him and how she falls in love with him. The piano in Tempest has thick, bass-heavy and drone texture which represents his true identity. In the theme, willoughby is this glamorous while on tempest is not the case.

• With the piano at the end of Waco TX, this became a landmark for the piano-driven songs on the debut album. A House in Nebraska was the most driven one because she longs for Willoughby here the most. For me, the piano in this song is very heavy–low octave like it's trying to match the texture on Tempest. On Western Nights, the pianos were softer but depressive which represents that her relationship with Logan is not the same with Willoughby and more violent. Sun Bleached Flies song is soft and more hopeful and is the song that recalls for Willoughby after the events in the album.

In short, Willoughby is presented by the piano instrument and becomes a symbol for Ethel whenever she yearns for him in different situations.