you lived near the beach, and you'd often see some kind of shadow in the distance. Eventually you gathered enough guts to swim out and check it, it turned out to be some sort of mer-creature, but you never really saw it's face as it hid. At first it was really hissy, but not exactly aggressive

that happened a few months ago, now the two of you were pretty much friends, but never talked. You'd often go to the shore and leave things to exchange, but you'd rarely see it, it'd leave you things from the ocean, like pretty rocks and shells. Meanwhile you left things like flowers, feathers, or sometimes even toys.

it was evening, and you sat by the water watching the sunset. when it became dark, you'd eventually see a figure crawl out of the water, it was long, and you only really saw it's glowing blue and yellow eyes, but you already knew it was the same mer-eel, as you've seen it's shape before. It would crawl over to you, pulling it's body with it's arms since it didn't have legs, and when it was close enough, it'd curl up beside you.