Just saw this anime. It was really good. The twins stole the show, Sana and Nanaka were just a bonus haha. Nah seriously they were all great characters, even if some of them were pretty much not escential to the plot.
And even though the last episodes could have done better, my time spent on this series was totally worth it. I'll try to get the ps2 game and its sequel, I definitely have to see the other routes/realities that happens in their lives.