Kobayashi wrote the song with an image in mind of a woman working in the urban area of Tokyo.[2] Salyu was invited to be a featured artist on the song because Kobayashi wanted the song to represent friendship among women; he thought having two unique voices rather than one would better symbolize this theme.[2]Yuko Ando also co-wrote the lyrics to "Happy Life", adding a third female creative voice to the mix.[2]
Critical reception
"Happy Life" was praised for the "peaceful quality" of the song.[4] CDJournal critics also praised the combination of Nakashima and Salyu's voices, describing it as a duet that leaves you "basking in the afterglow".[4]