Maybe the tail is real and her legs are fake?
When crossing the Atlantic ocean, Günter's airplane crashed and sank to the bottom of the sea, where he was discovered by a young sea princess on the day before her wedding to the
King of Herrings, whom she didn't love at all. So in order to avoid that forced marriage, she instead cavorted with the German preacher, keeping him alive by magically modifying his lungs so he could breathe underwater.
But the sea princess's parents, King Poseidon and Queen Nereide, found out about this and weren't happy at all. They talked very sternly to their daughter and took her video games away for several days. Günter was tied to the back of a seahorse with a bag over his head, and it swam off with him, carrying him to the shore of Florida where he was rescued by a gaggle of old ladies who were doing water gymnastics at the beach and thought he was cute.
Some time later, when Günter was strolling next to the shore, suddenly the King of Herrings stuck his head out of the water. "This is yours!" he barked, throwing a large egg to Günter. "Take it and get lost!"
Günter took the egg home and placed it in a bowl full of seawater. After some days it cracked, revealing an infant mermaid.
At first, Günter kept the creature in the sink and fed it shrimp. He didn't feel too well about all this, because of God and Jesus and
merpeople being
soulless heathens. But the mermaid grew until he had to put it in the bathtub. He taught it to talk and read using fantasy paperbacks and religious videos.
At some time, the mermaid said: "I want to be a highschool girl like human girls my age! It's so boring in this bathtub day after day." So Günter thought a bit and finally bought two artificial legs from a dubious Chinese internet retailer. One of the legs was to be put over the mermaid tail, the other one got glued on at the side to create the illusion of a bipedal human.
In order to keep his life's greatest sin secret, Günter fabricated the story that Gloria (as he'd decided to call his mermaid) was an ordinary human girl, and her mermaid tail was artificial, while in reality it's the other way round. And because such posts always get voted "autistic", the truth will never come to light. This shows that my story isn't a fairy tale but very real, because in fairy tales the good side always wins.