キャプテン・ムラサのケツアンカー is a Touhou Project arrange track produced by the doujin circle IOSYS, featured in maimai ORANGE PLUS since July 2015. The song is a high-energy remix of two themes from 東方星蓮船 〜 Undefined Fantastic Object, the stage 4 field theme 幽霊客船の時空を越えた旅 and the boss theme キャプテン・ムラサ, fused into a 190 BPM comedy number about Captain Minamitsu Murasa solving absurd plumbing emergencies with her signature "butt anchor" (ケツアンカー). The arrangement was handled by ARM (Youhei Kimura) with lyrics by 夕野ヨシミ (Takafumi Suzuki) and vocals by 山本椛 (Momiji Yamamoto), all core members of the IOSYS circle. Originally released on the IOSYS doujin album 東方アゲハ in 2010, the song later crossed over into the arcade rhythm game scene via maimai and subsequently appeared in CHUNITHM NEW. The official music video, produced by kouks (Dividice), is notable for its liberal use of mosaic pixelation that, according to the wiki, actually conceals nothing more than a cartoon duck, a joke befitting the track's irreverent tone. In maimai, the chart features a level 13 Master difficulty with a constant of 13.4, designed by はっぴー, while the Expert chart (level 11) was designed by 某S氏. An additional UTAGE (宴) chart titled なぞる順番を覚えるゲーム（上級編） ("Remember the Tracing Order Game, Advanced Course") was added during the MURASAKi PLUS era, though it is no longer playable as of current versions.