Hakumokuren ga Saita nara

Popular high schooler Shiina Masaki 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: Takahashi Nagi, 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)