This was a worthy watch. Visually, the basic, two-toned set throughout the show actually held things together rather than making it stale and boring. It gave a nice backdrop, allowing the characters to stand out.
I understand that the side characters were necessary to an extent, but there's really only one that's truly relevant. Nazuna makes a nice change in behavior after she meets Ko, though it's not significant enough to ruin her arc. I am disappointed in the lack of Ko's development because he's just as clueless at the end as he was in the beginning. Just out there flapping in the breeze, like a typical 14 year old boy, though in a show like this, it should have allowed him to develop at least a little.
All in all, I figure this is definitely someone looking for something different. It goes by fast with a steady storyline.