"Honjitsu wa Seiten Nari" (本日ハ晴天ナリ?) is the sixteenth single by Do As Infinity, released in 2003. The jacket shoot was done during a-nation 2003 before fans were allowed to enter the arena where the event was held. The jackets for both the CD and CD+DVD versions include Tomiko Van and Ryo Owatari holding bubble boards as if they were talking in comic-style. This song was considered the theme song to a-nation 2003.
This song was included in the band's compilation album Do the A-side.