I really enjoyed Mizuki's other work Crossroad, so I thought I might like CY-Believers as well. Unfortunately, it was really difficult to get into. The first chapter felt rushed and too much like it was jumping into the middle of the story and was taking too long to get to know anything about the characters. The art style was also difficult - it feels rough and the setting is vague. In fact, a huge number of panels have no background art at all and are just the characters in front of blank background or some tone patterns. This lack of setting makes the story feel groundless or like it's in a void, though there are establishing shots of locations from time to time.
But despite the difficulty with getting into the story, there was a definite feeling of promise, that it would be good if I persevered, so I pushed on and kept reading. And, indeed, the characters settled into place and the story fleshed out, and I began to care about what happened. It never became a particularly amazing book, but it was enjoyable enough, and a good deal more interesting than a lot of shoujo manga I have read, if only because the plot deviates somewhat from the usual.
Once Rui's father appears (he's a cloud of mystery that hangs over the first two volumes), the story really began to interest me. He's a great character, and though not comedic, rather funny. It's clear that he adores Rui, and the way he goes about demonstrating that is less than conventional. He, Rio, and Azuma provide the best parts of the story.