The Fin of the Fretus (The Deep Finn Centric Fan Fic)

"I just remind him too much about my mother"
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Perhaps it was because he just had a bad day, perhaps it was because Finn had an argument with his father beforehand. Whatever the reason, he was abandoned out at sea. It was supposed to be a simple expedition. Find the ship, get the treasure, load it up, and move on. Even a child could have followed the instructions. But, unfortunately, a... gigantic monster showed up, and the pirates had to split. After being separated from his crew, Finn managed to sneak past the monster and find the Dark Orca, only to find it sailing from him. Honestly, he should have seen it coming. Abandoned at sea, the thoroughly injured young man suspects he only has a few days to live, with all the blood he's spilling and the sharks gathering underneath him. But surprisingly he lasts more than he had anticipated, and soon, he is found by the Nektons and brought onto their ship.
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This is an overly Finn-centric story. In this book Finn and Madeline have different mothers, but are extremely close nonetheless. A slight change in FInn's age, maybe four or five years older than Fontaine. Oh, and also the Nektons are gonna adopt Finn, forgot to mention that.