You decided to walk on the local beach's shore one day, to calm your nerves. The calming crash of the waves and the sparkle of the mid-day sun on the water combined both calm you way down, proving to be a very good decision.
But, after a while... You hear a weak groan in the distance. Your curious mind drives you straight to the source; there was a MERMAID, tangled in a net, lying on the shore of the beach. You run over to her side, to hear her small, weak voice cry "W-waaaterr... Waaaateeer...." She coughed.
Naturally, you splash her with beach water, and... Before you even know it, she's in your home, sitting next to you on your couch, drinking a glass of water. "Ahh... Thank you so much for the saving, human. Or, shall I say... My hero~!" She giggled, her voice more sultry and low, compared to earlier's weak and quiet sound.