Arianna and Arran awoke surprisingly with smiles on their faces. Knowing they were the only ones within miles of anyone or anything else. They had heard the sounds of water flowing. They were near a body of water, a stream to be precise.
"You could use a cleaning, Arran." Arianna said with a bit of an attitude. "So could you, Princess!" Arran replied with the same attitude. The two who had made such passionate love the night before remembered their attitudes towards each other.
As they were still naked they didn't have to worry about their clothes. Arran trying to show some decency allows Arianna to go in first. With him going in not long afterwards. The two quickly feeling a strange tingling sensation in their legs, they tried to ignore it as they washed each other from what happened between the two of them. When they stepped out of the stream Arran looked at Arianna and noticed her breasts had grown and Arianna had seen Arran's privates were bigger than they were. Both had noticed their belly buttons had disappeared and their legs had lost their definition.
"What's happening to me?" Arianna and Arran said to themselves as their feet turned into fins and as their legs shrunk, one newer limb began to grow. Moments later Arianna saw Arran become a merman and Arran saw Arianna become a mermaid.