"H2-OH!" is about Mook and Charlie, two mismatched people who meet under odd circumstances. Mook was a competitive swimmer who lost several of her swimmer friends in an accident, causing her to become deathly afraid of water. When Mook is hit by Charlie's car and gets amnesia, Charlie takes her home to help her recuperate. Soon after, both of them start to see a ghost that appears wherever they are around water. Freaked out by the ghost in the water, they search for someone to help.