The Great King Jellyfish is a giant jellyfish which lives off the shore of Jellyfish Beach that, according to the local residents, will cause terror if not presented with a young maiden to hold.
After Akane received her Jellyfish Swimsuit and entered the long distance swim, she managed to reach the outcrop first, making her the winner. When she passed what she thought was the finishing line it turned out to be a tentacle of the Jellyfish King.
Worried for Akane's safety, Ranma (who'd followed Akane in a small rowing boat after being prevented from participating by the racing organisers) went to attack the Jellyfish King, however, the fight never occurred as Ranma was given a second place flag by the Jellyfish King, while Akane got the first place flag and a trophy.
As Akane is thrown up into the air and caught by the Jellyfish King, Ranma enquires what the organisers meant by giving a "young maiden" to the Jellyfish King, revealing they meant giving him one to hold. It is presumed that after holding Akane, the Jellyfish King returned to the ocean waiting to return the following year.
Despite seemingly being rather menacing in shadow when it initially grabbed Akane, the Jellyfish King is actually very gentle as shown by it playing with Akane by throwing her up into the air when she won the long distance swim.
Due to Akane winning the long distance swim, the Jellyfish King got to present her with a trophy and hold her. The Jellyfish King seemed to enjoy doing this and even posed for a photograph with Akane.
- There is mention of a "Great Jellyfish Queen", however, whether this is the Jellyfish King's "wife" or just a giant female Jellyfish is debatable.