 Toyosaki , Hikasa , Satō , and Kotobuki performed the insert song , a song that occurs within the episodes of the anime , " Fuwa Fuwa Time " for K @-@ On ! . It was released as a single on May 20 , 2009 . On June 17 , 2009 , Toyosaki released a K @-@ On ! image song single named after her K @-@ On ! character Yui Hirasawa . The single ranked third on Oricon 's weekly singles chart during the week of June 15 to 21 , selling 31 @,@ 384 copies . 
