The band embarked on the CNBLUE Spring Live 2016 "We're Like a Puzzle" arena tour, where they held four concerts in Aichi, Tokyo, and Osaka.

Due to the band's fifth anniversary since its major-label debut in Japan, Jung took interest in composing a song about marriage.

In crafting the song, Jung sought to create "pop melodies and lyrics with a story, but also linked to the visual, such as a CD jacket and music video".

[4] Described as a "bright" alternative rock and synthpop track, it is the band's first wedding-themed song; the lyrics revolves around "eternal love".

[1] "Be My Lover" was written by Lee Jong-hyun, who also composed the track alongside Kim Jae-yang and Park Hyun-woo; it was arranged by the latter two.

[5] In order to express its "poetic sentiment", the song is sung entirely in English to capture the "emotions, feelings, and delicate nuances" of the lyrics.

[10] "Puzzle" was released on May 11 in four editions: Regular Edition; Limited Edition A with bonus DVD content that includes multi-angle performance footage of CNBLUE's Spring Love 2015 "White" concert that took place at the Yokohama Arena, the music video for the single, and a special feature; Limited Edition B with bonus DVD content that includes performance footage of the 2016 Arena Tour "Be a Supernova" concert that took place at the Osaka-jō Hall; and Boice Limited Edition with bonus DVD content that includes performance footage of "Let's Go Crazy", "Heart Song", "Stay Sober", "Foxy", "White", and "Radio" from the CNBLUE Official Fan Meeting 2015 Boice "Natsu Matsuri" event, and the Boice Special Movie "Bouquet Making".

[11][12] "Puzzle" sold 21,304 copies in its first day of release and ranked number three on the daily Oricon Singles Chart.