Nobita's Mermaid Legend

To prove that Suneo is wrong and the Mermaids were true, Nobita and Doraemon went 100 years ago. Nobita turns himself into a merman, but he and Doraemon are attacked by a shark and end up on a boat. It turns out that the "mermaid" Johann saw was merman-Nobita himself; Even the "mermaid" it was mermaid-Michaela!