Rub-a-Dub-Dub! There's a Pervert in the Tub
Maboroshi no Happodaikarin wo Sagase
"Happosai has forgotten his ultimate technique, the Happo Fire Burst. Ranma and the others try to get their hands on the scroll that holds the secret to the technique, but it's sealed away in the middle of an open-air hot spring where Akane is bathing! " (source)