Shinnosuke's grandfather

Shinnosuke's grandfather used to be a zookeeper near Ryugenzawa before all his animals escaped into the forest. When they drank the water of life, they became monstrously huge and he along with Shinnosuke kept the animals away from the village and the people away from the forest. But as he grew older, he lost a lot of strength and remains in his bed nearly every day. After Akane arrives and stays with them for a bit, he drops several hints in Akane and Shinnosuke's presence about their mutual feelings for each other, which they all respond to by jointly throwing him in the air. He knows a lot about the Yamata no Orochi and its relationship with the Water of Life, although it appears that he does not actually see it until it awakens shortly after Akane arrives. When the Water of Life springs begin to dry up, he attempts to take on the Orochi by himself while disguised as a woman, but fails. After Ranma and Ryoga appear, he supervises the combined effort against the Orochi.

OVA
In the OVA, the animals that escaped into Ryugenzawa used to be his pets. When Shinnosuke loses his memory his grandfather will use his "Megaton Punch" to remind him. His voice was supplied by Takeshi Aono in the original Japanese and by French Tickner in the English dub.