Once

"Once" is a song by Hitomi Harada that served as the opening theme (OP 1) for the 2011 television anime A Dark Rabbit Has Seven Lives (Itsuka Tenma no Kuro Usagi), which was animated by Zexcs.

Released by Frontier Works on July 27, 2011 as Harada's debut single, it was also issued as Once - EP and featured the B-side "Yume Miru Sekai." Takuya Watanabe wrote and arranged the song, and the single reached No. 39 on Oricon's weekly singles chart, remaining there for three weeks.