Makoto reveals to Nagisa that he has great problems with Haruka stripping all the time. As he explains , he went out shopping with Haru the day before and Haru, upon spotting a large fish tank, left Makoto behind to strip and try to get inside. When stopped, Haru always becomes irritated. To discover why Haru behaves this way, Nagisa decides that they should conduct an experiment. (thetvdb.com)