Sea Skin (Poseidon x Reader) Record of Ragnarök

No one understood the Sea God quite as much as this one particular fish did. Oftentimes following after him whilst he patrolled his domain. It was fond of his presence as much as he was of it. Choosing to stay by his side despite the weapon in his hand that he often carried. This fish couldn't have been any more ordinary. A simple creature that would wait for him despite the season change. Going as far if it meant they would be by each other's side.
A small insignificance he should have brushed away long ago.
Yet it did nothing to hinder the small borrow growing in his chest as time wore on. A small haven for the fish to curl up in and make home of the cold heart residing within him.

But time was as cruel as the waters itself as sailors called into shore that one fateful day.
But why should the Sea God care? The absence of one fish meant nothing compared to the hordes of children vacating his water daily.
One dead fish meant nothing to the Sea God. He would have to move on like everything else in his immortal life. Yet why did it still hurt? Why when salt water rushed through the hole in his chest did it still painfully remind him...of you?

[In which our fish/reader is reincarnated] SIMILAR TO THE LITTLE MERMAID.