From the introduction:
Welcome to Mega W’s magical realm – a large, ordinary Japanese highschool with an even ratio of male and female students. Up until now, the worst thing to happen here has been some students violating the strict rules about personal appearance that are imposed by the education system. It’s not haunted, there are no super-powered battles in the halls, and there’s no secretive ninja cabal infiltrating it. Unfortunately for the students and faculty, though, the school infirmary gets its medicine from an irresponsible, drunken genius of a pharmacist who’s just made a breakthrough in her quest to develop a rapid-acting oral hair dye. Unfortunately for the world, the moment she cleared the animal trials for her drug she got extremely drunk and sent all four thousand bottles of her prototype Color Change (CHC for short) to the school you’ve found yourself in. She’s turned up to try and rectify the mistake by tracking the stuff down, even enlisting the help of one of the students in the process, but a pair of delinquents has already stumbled onto the full supply and decided to have fun with it by spreading it around.