Deep in Abyss is the debut single tied to the anime series Made in Abyss (メイドインアビス), serving as its first opening theme, with the episode 1 twist of being used as the ending theme instead. The song is performed in-character by the series' two protagonists: Riko (voiced by Miyu Tomita) and Reg (voiced by Mariya Ise). Composed jointly by KanadeYUK and Masahiro "Godspeed" Aoki, the latter a familiar name to SEGA rhythm game players for his maimai commission "UniTas" and the CHUNITHM track "Gate of Fate", with arrangement by KanadeYUK and lyrics by hotaru, the piece balances a gentle, curious melody with the ominous undertones that define the series' atmosphere. Released as a single in 2017, Deep in Abyss arrived in maimai as part of the FiNALE edition on March 22, 2019, classified under the POPS & ANIME category. The song was later delisted on September 16, 2021, and its availability was always restricted to Japanese arcade cabinets due to anime licensing limitations. The in-game version uses a shortened edit (1:28 compared to the full single's 2:26). The Expert chart was designed by ロシェ@ペンギン and the Master chart by ぴちネコ.