I absolutely love the story, but the ending was quite rush. I wish they could've decided for a season 2, at least they can make that anime into an action anime.
+ I wish they had made more scenes of Yu and Nao after his return.
and also the episode 6 was kinda useless after Yu went back in time to save her sister, that part right there was actually the best scene but I felt really, disturb because of that. I wish they could've stick to the story that her sister is dead.
But overall the anime is superb, Story, Art, Sound, Character, Enjoyment 10/10. But overall is 9 for rushing the ending.