 Misia decided to write lyrics that revolved around the dedication of the ōoku and the outpouring of love for their one and only "shōgun".EMTG Music's Yūichi Hirayama stated about "Deepness" that "the message is in the sound of the song itself" and compared it to the "crisp" sound of Misia's "Snow Song" (2003).Hirayama described the song as being the "ideal vehicle" for Misia's voice.