S1·E52 The Sky Flying Zorori Castle

Zorori and the boars end up in a castle flying in the sky that turns out to be none other than Zorori Castle. The castle explains that the mermaids grew homesick and then set the castle free. The castle got lonely and decided to find a new master, and managed to fish his old master back. Zorori agrees to be the castle's master again and for several days all goes well. Then the castle runs out of food because Ishishi and Noshishi are gluttons. When attempting to find more food by going back down to Earth, the castle freaks out and imprisons them all, for fear of being left alone again.