There's X and there's XS|Chemical X Trilogy (Book III)

For ten years the Powerpuff Girls and the Rowdyruff Boys lived without their powers under the same roof and going to the same school in relative peace. Then it all comes to a violent end. First the Professor becomes mysteriously ill, then their pet chimp Jojo, after a strange violent outburst, mysteriously disappears. Not long after this, Brick receives a "mysterious" note to come to a "mysterious" meeting at the park from an anonymous sender, but meeting with a monkey back to his redundant abuse of the English Language is the least of the mysteries. As the teens get their X powers back, a long and complicated psychological game is thrown at all those living in the Utonium household. Who are those responsible and why become darker questions the more it all plays out.

Part III of the Chemical X Trilogy.