ga Kitara" was written by Yūji Sakamoto and Daisuke Hinata, both of whom had worked with Matsu. Sakamoto had been Tokyo Love Storys screenwriter and Hinata had been in charge of the music of Long Vacation. Hinata provided the music and arrangement to "Ashita, Haru ga Kitara". The track was recorded at the Hyper Image Studio in Santa Monica, California, in January 1997. Hinata himself mixed the audio while Steve Hall mastered it. Cagnet provided instrumentation to the song. The record was produced by Kozo Nagayama, who had also produced Long Vacation. Initially, another song was selected to be released as Matsu's debut single. However, it was scrapped for unknown reasons and "Ashita, Haru ga Kitara" was selected instead. Matsu debuted the song on radio on February 14, 1997, and the single was physically released on March 21, 1997, through BMG Japan as an 8 cm CD single. Composition "Ashita, Haru ga Kitara" is a mid-tempo J-pop track with a "gentle melody", that lasts for 4 minutes and 13 seconds. According to the original score published by Doremi Music Publishing, it is composed in the key of B minor and in the common verse-chorus song structure with a tempo of 110 beats per minute. The track opens with an instrumental introduction with a chord progression of Gmaj7–Fm7–Bm. As it reaches the chorus, the progression shifts to G–A–Fm–Bm7. The same pattern is repeated throughout the song. The lyrics of the song, written from the perspective of a girl, sees her recollect the memories of her love with a member of her high school baseball team and how she hopes to meet him again "tomorrow, if spring comes". Upon the album's release, Yoshitake Maeda, writing for BMG Japan, commented that Sakamoto probably reminisced on his teenage years through the song. The b-side of the single "Zutto... Iyō yo" was written by Matsu and produced by Hinata. Matsu decided to give it the theme of three girls going out for a drive. However, she commented that no matter how others looked at it, it seemed as if the song is about two girls. The song opens with an "electro" introduction and utilizes a warped guitar throughout. In addition to the two songs, the single also featured the original karaoke track to "Ashita, Haru ga Kitara". An LP titled Remix Hyper Bug containing remixes of "Ashita, Haru ga Kitara" by DJ Craig William—"Ashita, Haru