"Smily / Biidama" (Smily / ビー玉; Smily / Marble) is Ai Otsuka's eighth single, which was released on 11 May 2005. "Smily" was used in a television commercial for Lion's Ban Powder Spray, while "Biidama" is being used in a commercial for Shokubutsu Monogatari Herb Blend shampoo, also by Lion. Otsuka appears in both commercials.
The single debuted at number one on the daily Oricon chart. By the end of its first week, it sold 110,512 copies and was number one on the Oricon weekly chart. The single sold 308,338 copies in 2005 and was the #26 single of that year. The current figures show it has sold 310,323 units in total, making it Otsuka's third highest selling single.