Twelve years after the final OVA was shown, and the end of the manga, a new piece of Ranma ½ animation was made for the "It's a Rumic World" exhibition of Rumiko Takahashi's artwork. The new 30 minute special is based on the "Nightmare! Incense of Spring Sleep" manga story from volume 34, and was shown on odd numbered days at the "It's A Rumic World" exhibition in Tokyo from July 30th to August 11th.—http://myanimelist.net
Akane is accidentally cursed by Master Happosai, and falls into a long, deep sleep in which Ranma is usually the protagonist. The problem is that all this happens in the Furinkan school, causing chaos and destroying everything in its path. The new 30 minute special is based on the "Nightmare. Incense of Spring Sleep" manga story from volume 34.—Wikipedia