Most of the anime does not contribute to the story in any way, it's just filling time. There is close to no character development and when there is, it's just rushed and unprecedented.
The ending with Aname and Hikari was just convenient, but there was no purpose to it. No message. No logic. The author just needed a candidate to go against Nagisa for Étoile and that was the most built up couple there was. The author even used the amnesia cliché to try to maybe add some tension but it was weak, poorly executed and unnecessary. An ending with Yaya would have made more sense.
As for Shizuma-Nagisa ending, that was right but rushed. So much of the anime is dedicated on trivial things and so little happened to develop each character, then, at the end you've got so many events happening back to back; totally going against the previously established pace and most of them having unconvincing justification because it's all too rushed.
Oh, and another thing:
all the girls are lesbians.
It'd be alright if there was a few. I get it. But, seriously, all the freaking school is lesbian?
That's beyond unrealistic.
All in all, this series get a 2/5. I would not advise anyone to watch it but it's not so horrible I want to unsee it. The universe created was interesting and the Nagisa-Shizuma relationship was interesting, at first, but then poorly developed. It had some nice elements to it but the ending was too rushed. Maybe if the author took more time to execute his ending, with more character development, it would have been better or if he removed the time fillers and added more real story...
