The sub-genres of Fantasy

After four years since their disappearance, The Powerpuff girls Z realize that their new classmates are nothing more, nothing less than the Rowdyruff boys Z! Nevertheless, they're not what they expected. The boys don't seem to remember them and act like normal boys! What's behind this mystery? Are the boys just playing fool and planning to do something bad? And if they're telling the truth, what happened to them?