This a story of a boy meeting a girl and their relationship. One of the things that may discourage people from this anime is the fact that there's nothing particularly new or innovative, but just the same, this show tells a story that I found to be emotional, meaningful, and enjoyable.
The chemistry between the two main characters is there instantly, and it's a believable connection as well. Tazuna and Koyori are reliant upon each other in the end. Tazuna keeps Koyori alive and Koyori gives him the power to fight off their enemies.
Also just as important are the moments between battles, with two teenagers being teenagers. The romance is not very subtle, but there's no denying that it's endearing and cute. It made me want to cheer for them more and more with each passing episode.
Also augmenting to the show is a soundtrack that combines classical music with electronic music. The piano and the beats work well with each other and only further make the tone of the moment noticeable. You can't mistake what the mood is when a soundtrack is playing.
The art style can take some time to adjust to, but there is a certain beauty to it. the colors are vibrant, the animations are well-done.
I hear that this anime borrows from another anime titled "K." I don't know this to be true, so I'll have to look "K" up to see. Otherwise, I'm not really sure what people are complaining about.
As a person who's quiet and a bit shy, I found myself latching onto the show and its characters instantly.