Etude Op 10-4

The song flashed by very briefly in PHOENIX's first teaser, but its title and full content were properly revealed at PlayX4 in May 2023, during the tournament champion's exhibition, shown alongside the D25 chart. Because the official BGA took a while to release, for a time the only available audio was a live recording with audience chatter bleeding through, which sparked running jokes that "the lyrics were missing." Chart maker EXC left behind two remarks from the gala that became community memes: one about how crucial stamina management is on this song, and one where he questioned his own difficulty rating.

The original etude carries a subtitle evoking a chase, so the BGA tells the story of a phantom thief who steals a music-note jewel and the detective who pursues her. According to BAMI, both characters are women with no proper names (the avatar shop labels them Kaito M and Detective P). Many players compare its style to Sugar Plum. In the newspaper and chalkboard scenes, nods to Switronic and Annihilator Method appear as easter eggs.

The song ships with a wide spread: Single S4, S7, S11, S16, and S22, plus Double D13, D17, and D25. SUNNY authored the lower and mid charts along with D13 and D17, while EXC handled S22 and D25. S22 was called too hard for its level from the moment it was shown. D17 plays as a comfortable level-17 longnote chart until the final roughly seven seconds, when a brutal ending well beyond its level drops, which is why it is widely seen as underleveled. D25 stirred difficulty controversy and its closing stretch was toned down for the official release; alongside もぺもぺ and ULTIMATUM it belongs to the top-tier level-25 group nicknamed "모얼추."