[1] In May 2020, prior to the release of the Day6's album The Book of Us: The Demon, it was announced that the group would cancel promotions of the album and go on hiatus due to the mental health issues of some members, later revealed to be leader Sungjin and guitarist Jae.
Even of Day was formed with the remaining active members: bassist Young K, keyboardist Wonpil, and drummer Dowoon.
[3] On August 11, JYPE officially introduced Day6's first sub-unit project, Even of Day, five years since their debut.
JYPE released a teaser image announcing the unit on Day6's social media pages.
The Book of Us: Gluon, alongside its lead single "Where the Sea Sleeps," was released on August 31.