Shirō Sagisu
"Kioku" was co-written by Misia and Gorō Matsui, composed by Korean composer and record producer BZ4U and produced by Shirō Sagisu. The song is composed in the key of B-flat major and set to a common time tempo of 65 beats per minute. Misia's vocals span from F3 to E5 in modal voice, and up to G5 in head voice. TV Asashi producer Yumiko Miwa tasked Misia to write a song that would convey "hope and sympathy". Misia penned the lyrics to "Kioku" shortly following the 2011 Tōhoku earthquake and tsunami, and she describes thinking of recent events while writing the song.