The lead single, "Let's Fall in Love for the Night" peaked at numbers 17 and 24 on the US Billboard Alternative Songs and Rock Airplay charts, respectively.

The EP marked Finneas' first solo release after co-writing and producing material for his sister Billie Eilish for several years.

[7] The song features minimalist production of bass guitar, piano, drums, layered harmonies, an aggressive beat, and synthesizer.

[16][17] The song's lyrics are about a girl Finneas has never met in person but finds comfort by dreaming about being together with her in an alternate universe, but only temporarily.

[19][20][21] The sound of typing and sending messages is heard for the majority of the song,[19][22] with it being almost entirely composed of real texts between Finneas and a former lover.

[26][27] Blood Harmony was released by Finneas' record label OYOY, and distributed by AWAL, on October 4, 2019.

[5] That same month, Finneas performed a majority of Blood Harmony's songs at the Austin City Limits Music Festival.

[14] On February 3, 2020, he performed "Let's Fall in Love for the Night" on The Tonight Show Starring Jimmy Fallon and was joined by a live band.

[43] Will Richards writing for NME, said the songs on Blood Harmony are "exquisite" and have an update "with fresh, modern production tweaks".

[3] For Billboard magazine, Glenn Rowley praised the EP, saying "Finneas' work as a solo artist is decidedly brighter, his soulful voice tying each song together as his lyrics swings through the vast spectrum of human emotion".

[6] Nicole Almeida of Atwood Magazine wrote that Blood Harmony is the "most transitional point of Finneas' career".