My Days with My Sister, Melting with Sadness

Anehame: Ore no Hatsukoi ga Jisshi na Wake ga Nai

Akira Sakagami was preparing to ask his classmate Nana Shirayuki out on a date when his sister Rio suddenly arrives, moving back in with Akira due to her housing situation. This complicates things because Rio was his first love. Then, Rio points out that Shirayuki looks really similar to her. Now he can't help but see Shirayuiki as his sister.