Refvain (リフヴェイン) is a maimai DX original track composed, arranged, and written by Aoris (青栗鼠) and sung by sekai. It debuted in maimai でらっくす FESTiVAL PLUS in June 2023 as part of the Sky Street Area 4 (スカイストリートちほー4) unlockable song set, alongside other story-driven originals. The song's music video was produced by the artists しょうけい and 米室. Thematically, Refvain is anchored by a dense flavor text, a dark speculative-fiction vignette about an experiment subject designated "No. 31," renamed Noah by a mysterious director named Akatsuki. She is conditioned to time-travel to 2021 and assassinate three targets: a politician, a chemical-company executive, and a prophet. After completing her mission, her body fades, but she awakens once more in the same concrete room, the director's face identical to the prophet she killed, suggesting an endless, looping cycle. The title itself appears to blend "refrain" (リフレイン) with "vein" or "vain," mirroring the song's fixation on repetition, puppetry, and futility. The lyrics, written by Aoris, reinforce this with motifs of amnesia, marionette strings, reincarnation, and decay. On the rhythm-game side, the Master chart, designed by じゃこレモン, sits at level 13+ (13.6) with 643 notes across all five DX note types, while the Expert chart by みそかつ侍 carries a 10+ (10.6) rating with 383 notes. The song has remained available across subsequent maimai versions, default-unlocked from BUDDiES PLUS onward.