Ariel is mostly not a real story. It could be from a fantasy world, a product of someone's creativity. There's no historical or factual basis for it to be considered real.
One idea could be that Ariel discovers a new sea creature that has the ability to tickle with its tentacles. As she explores this new discovery, she gets into some ticklish situations. For example, when she tries to study it closer, the creature playfully tickles her fins. Another idea is that Ariel and her friends play a tickle - based game in the underwater kingdom. They could have rules like the first one to get tickled three times loses. This could lead to a lot of laughter and fun among them.
In this fanfic, Moana is on a new voyage and gets lost in a mysterious part of the ocean. She ends up near Ariel's territory. Ariel, who has always been interested in humans, approaches Moana. At first, Moana is a bit startled by a mermaid but soon realizes they share a common love for the ocean. They start to exchange knowledge. Ariel shows Moana some of the amazing underwater wonders she has never seen before, and Moana teaches Ariel about the stars that help her navigate. Together, they face a sea monster that is causing trouble in both their areas of the ocean.
Ariel is purely a creation of imagination. There's no real-life event or person that it's based on. It's a classic example of a fictional tale designed to capture the hearts and minds of the audience.