Cirno's Perfect Math Class is a viral music video and song produced by the doujin circle IOSYS, based on the character Cirno from the Touhou Project series. Released in 2008, the video features a manic, catchy tune where Cirno attempts to teach a math class despite her reputation as an 'idiot,' famously symbolized by the circled number nine (⑨). The meme gained massive popularity on platforms like Nico Nico Douga and YouTube, characterized by its high-energy dance and nonsensical logic. Today, the template is used to represent moments of confidently incorrect math, celebrating the baka archetype, or simply paying homage to classic internet anime culture.