One day, I was rather curious about how she started out. Now, she did have her performance in the ending theme for Season 1 of the aforementioned "Chūnibyō demo Koi ga Shitai!" during its time in 2012, but her debut single as a solo performer came in April 2013 with "Nanatsu no Umi yori Kimi no Umi" (Your Sea More Than The Seven Seas).
Seeing a few of her music videos, she definitely has her own style but I think she really made a splash for the official video for this first single of hers. I recently watched some YouTube videos of Soviet-era television, and yes, perhaps the intro got some inspiration from that medium. And then the song launches into a carnival-like atmosphere of craziness that pulls in circus music, heavy metal and maybe even ska. Not sure whether the people around her had already figured her out but "Nanatsu" and the video certainly come across as pure Sumipe earworm.