It's a Thrill! The Terrible Overhead Cooler Urusei Yatsura : Season 9 Episode 4

It's a sweltering summer day, and everyone's all hot and bothered, except Lum. She's staying cool with an alien cooler that produces a floating, mind-controlled ice block. She gives some to her classmates, but warns them that stress will make the blocks of ice grow and come crashing down on their heads. If the stress levels reach their peak, then the user's fantasies will become projected in the ice, which opens up all sorts of impure possibilities for Ataru.