ウミユリ海底譚 (Umiyuri Kaiteitan) is a VOCALOID track by producer n-buna featuring Hatsune Miku (初音ミク) on vocals, with original video art by あわしま. The song arrived in maimai as part of the ORANGE PLUS update on May 14, 2015, initially listed under the niconico genre before being reclassified as niconico & VOCALOID from PiNK onward. Its BPM of 120 is deliberately halved, one of the few maimai tracks programmed this way, giving the composition a spacious, half-time drift that suits its seabed imagery. The title translates roughly to "Sea Lily海底 Tale," evoking the swaying of crinoids (sea lilies) in an underwater current. The Master chart, designed by はっぴー (Happy), is among the most recognizable in the maimai community thanks to its signature "ウミユリ配置" (Umiyuri pattern), a demanding sequence beginning around combo 301 that alternates slides and taps, deliberately exploiting the game's slide-start delay where slides register one beat after the note is triggered. This pattern became so emblematic that a dedicated UTAGE practice chart titled "ウミユリ練習譚" (Umiyuri Practice Tale) was added in maimai DX PRiSM (September 2024), allowing players to build up to the full pattern through progressively denser slide arrangements. The Expert chart, designed by 某S氏, offers a gentler introduction to the song's melodic structure. The Master chart has undergone multiple level revisions across maimai versions, from 11 in the ORANGE+ era to 13 as of FESTIVAL, reflecting both the game's evolving difficulty scale and the chart's enduring technical demand. In October 2022, the DX theoretical maximum score was first recorded. Beyond maimai, the song has appeared in CHUNITHM PLUS (2016) and オンゲキ R.E.D. (2021), and was also featured in Hatsune Miku -Project DIVA- X with an official English lyric translation.