Hakumokuren ga Saita nara

Popular high school student Masaki Shiina only has one girl on his mind—"Nagi," who disappeared after his love confession years ago. One day, an unusual pair of twins transferred to Shiina's school: Nagi Takahashi, the brother, and Nagisa, the sister. Confident that Nagisa is "Nagi," Shiina is elated to find his love again. The only problem is that she doesn't remember him at all. (Source: Bliss)