つるぺったん is a comedic Touhou Project arrange track by the doujin circle Silver Forest, originally released on their 2007 album 東方萃奏楽 (Touhou Suisou Gaku). The song is an arrangement of 竹取飛翔 ～ Lunatic Princess, the final boss theme of 東方永夜抄 ～ Imperishable Night (2004), the theme associated with Kaguya. But where the original is an elegant, atmospheric piece, Silver Forest reimagines it as an unabashedly silly gag song: the lyrics, written by bit and performed by vocalist Kana, depict Suika Ibuki stalking Reimu Hakurei and mercilessly ribbing her about having a flat chest, a long-running fan meme within the Touhou community. The title つるぺったん itself is a playful compound: つる (tsuru, "smooth") + ぺったん (pettan, the sound of something flat making contact), forming a teasing slang term for flat-chestedness. The lyrics are densely referential, weaving in nods to other songs including ふたりのもじぴったん (from the puzzle game ことばのパズル もじぴったん), レッツゴー！陰陽師 (from 新豪血寺一族), エージェント夜を往く (from THE iDOLM@STER), and 巫女みこナース・愛のテーマ. The in-game achievement title unlocked at Rank A reads つるぺったって言うなぁ(T T), "Don't call me tsurupetta (T T)", completing the joke. つるぺったん first appeared in a SEGA rhythm game via CHUNITHM STAR PLUS in October 2018 before crossing over to maimai with the FESTiVAL PLUS update on June 8, 2023 (with staggered releases for the Asian and Chinese regions later that year). Its maimai Master chart, designed by 鳩ホルダー (Hato holder), clocks in at exactly 666 total notes, a mischievous detail that suits the song's irreverent character. The chart originally launched as Level 12+ and was adjusted to Level 12 starting from the BUDDiES PLUS revision. The Expert chart was designed by カマボコ君 (Kamaboko-kun).