Bokura No Koi Wa Shi Ni Itaru Yamai No You De

As children, Aki became acquainted with a four-year old Akane. Meanwhile, Sora confessed to Akane that he'll propose to her when she turns 18. Unfortunately, he died in a traffic accident. He then appears before Akane, Masaru, Aki's younger twin, with the voice, figure and everything else like him. Akane, had to confront the twisted love and affection given to her by Masaru, instead of Aki from...?!