"Kairos" is a maimai original song composed by South Korean producer ARForest (#ffffff records) with vocals by nayuta, created as the Perfect Challenge track for Skystreet Area 4 (スカイストリートちほー4) in maimai でらっくす FESTiVAL PLUS. Released on June 22, 2023, the song marks both ARForest's and nayuta's debut contributions to the maimai series, following their earlier collaboration on "Hibiki" for Konami's pop'n music UniLab. The title "Kairos" draws from Greek mythology, Kairos (Καιρός) is the god of opportunity and the fleeting favorable moment, and the word itself denotes a qualitative sense of "time" distinct from the sequential Chronos. This thematics carries into the song's flavortext and lyrics, which depict two figures watching fragments of passing time in a world shaped by the C204 incident, questioning whether the place they have arrived at is truly the world they wished for. Clocking in at a brisk 200 BPM, the track pairs ARForest's driving electronic arrangement with nayuta's ethereal vocal delivery. The jacket illustration was created by Masako Wada, with video production by 緒河 秋 (credited as Roly/bikku in the English sources). The MASTER chart, designed by Jack, notably launched at level 13+ (difficulty constant 13.7) and underwent multiple downward adjustments, to 13.6 in BUDDiES PLUS, then to 13.5 in PRiSM, where it was also reclassified as a straight level 13. This makes Kairos the lowest-level MASTER chart among all Perfect Challenge songs to date. The EXPERT chart, designed by サファ太 (Safata), sits at level 11. From BUDDiES PLUS onward, the song is unlocked by default, removing the area-progression requirement.