L9 (pronounced "エルナイン" / "L-nine") is a high-energy progressive instrumental track by paraoka that joined the maimai lineup with the ORANGE PLUS update on March 19, 2015. The song traces its origins to the 2001 B-1 CLimaX System-C Be-Music Source song contest, where it was one of the winning entries, a pedigree that predates its arcade rhythm-game career by over a decade. Musically, L9 is a relentless barrage of dense synthesizer arpeggios, rapid-fire drum patterns, and a driving bassline at a blistering 256 BPM. The track is purely instrumental with no vocals, sustaining its intensity across a 2:00 runtime. An extended version later appeared on the Diverse System compilation Side-c., and the maimai cut is based on that version with a lengthened intro. In the maimai ecosystem, L9 is best known for its demanding MASTER chart, designed by ロシェ@ペンギン (Rocher@penguin). With a level rating of 13+ and a difficulty constant of 13.7, it ranks among the most challenging standard charts in the game. The EXPERT chart, crafted by Revo@LC vs Jack, was originally credited under the collaborative alias "合作だよ" before PRiSM PLUS updated the attribution to the individual designers. L9's difficulty levels have been adjusted multiple times across maimai versions, the MASTER chart began at level 12 in ORANGE+ and climbed to 13+ by FESTiVAL, reflecting the track's evolving status in the difficulty hierarchy. L9's reach extends beyond maimai into several other rhythm games: it appears in SEGA's CHUNITHM (with its own WORLD'S END and ULTIMA charts), オンゲキ, and even KONAMI's SOUND VOLTEX series. Within the BMS community, the song has achieved cult status, inspiring remixes such as naotyu-'s "L99" and a series of notorious parody charts.