it's an attack, isn't it?. depending on how powerful it is, you can just chop your opponents HP down bit by bit and they can't do anything because you block their actions just by using the move. that's why it probably has a downside, like low accuracy or PP, or it works differently from how we think it does.Seemed to me that the downfall is that you are also unable to do anything.
by the way, just wanted to get out that I think Koromori looks adorable. I'm also not disapointed that it's Psychic/Flying, just surprised because it seemed so unlikely compared to other typings (like Dark, or even poison).