Cirno's Perfect Math Class (チルノのパーフェクトさんすう教室) is one of the most widely recognized Touhou doujin arrange tracks to appear in a rhythm game. Produced by ARM and Yoshimi Yuno (夕野ヨシミ) of the circle IOSYS, a group that defined much of the late-2000s Touhou parody and arrange sound, and sung by vocalist miko, the track reworks Cirno's stage theme Otenba Koimusume (おてんば恋娘 / Naughty Girl) from Touhou Koumakyou ~ the Embodiment of Scarlet Devil (2002) into a high-speed comedic number. The lyrics cast Cirno, the ice fairy and Stage 2 boss, as an absurdly overconfident student who brags about her arithmetic prowess while making elementary errors, a gag that plays directly into her long-standing fandom identity as the "⑨" (a Japanese internet shorthand for "fool"). This self-aware humor paired with a relentlessly catchy melody and rapid-fire vocal delivery made the song a fixture of Touhou MAD culture long before it crossed into the arcade rhythm-game space. maimai players first encountered the song on July 11, 2013 as part of the GreeN version, where it was initially playable with Standard (ST) charts only. The Standard Master chart, originally rated at level 10 in GreeN, has seen its difficulty rating climb steadily across major version updates, settling at 13.3 by the PRiSM+ era, a visible record of how maimai's chart-difficulty calibration has shifted over more than a decade. On September 18, 2025, a full set of DX (でらっくす) charts arrived with the CiRCLE version, unlockable through the stamp card system and featuring new note distributions unique to the DX format, including a notably hold-heavy Expert chart designed by サファ太.