A substitute for her sister, eh? She may have thought of it that way, but I'm glad that he accepted her as herself rather than just as a substitute, I really like that.
Having to break up with your girlfriend at the beginning seemed like it affected him quite a bit, so at least he has a chance to be happy again with a new girlfriend.
That ending though. Well hey, they are sisters, so she still has room to grow in future?
The sadistic part of me wants to see the face of Haruna when she someday comes back to town for the weeding of her sisters, sees who she is marrying and realizes what life she could have had...