Ether Second is a maimai original song by Akira Complex, created as a direct sequel to Ether Strike, a track originally contributed to the rhythm game Arcaea during its cross-title collaboration with maimai. Released posthumously after Complex's passing in June 2023, it stands as one of the composer's final works. The track moves at 150 BPM and carries forward the atmospheric, driving sound that defined its predecessor, blending crisp synth leads with a relentless pulse. Within the game's 7sRef area storyline, Ether Second accompanies the gatekeeper Helblau (ヘルブラオ), keeper of the "blue door." The in-game flavor text reveals a narrative tension: Helblau is openly fascinated by the world beyond the door she guards, drawing concern from the observer Flöhnspüler (フルーンシュピラー), who warns that such curiosity is dangerous for beings whose role is to keep watch, not to cross over. This thematic contrast, duty versus the allure of the unknown, mirrors the song's relationship to Ether Strike, framing it as a return to a familiar yet unexplored space. The song's jacket and movie visuals were produced by Mi'yuki and Tobi. Across its DX chart set, the Expert chart was designed by はっぴー, while the Master chart (level 13+, constant 13.9) was designed by サファ太 and packs a dense 855-note count with a notably high 61 Break notes, making it a demanding technical challenge within the BUDDiES lineup.