Lyrically it deals with the group saying "sorry" towards each other, using the Japanese word "Gomennasai"; hence the title. "Gomenasai" received mixed to favorable reviews from music critics, who felt it was gentle and one of the group's best vocal songs to date, while some felt it was similar to other ballads.
The song explores themes of apology through lyrics that use the Japanese word "Gomennasai," which is reflected in the title. Music critics had varying opinions on the song's quality, with some praising its gentle nature and vocal performance while others found it similar to previous ballads.