[koumori]

According to an unlisted youtube video that seems to be the Summer Again audio, the song was composed by Hajime Kato. He's someone who worked with the composer of Nonfiction, Hisashi Koyama, in the past as well - but this year is the first time either have worked with Ayu, so I'm really curious about what it'll sound like now! Credit to truehappiness and sen@AHS Discord for catching this detail.

If anyone is wondering, the video is now unavailable and it was when the URL was found as well - no one has listened to it! Yet...