When you first became a sailor, you weren't the best swimmer- you almost drownd if it hadn't been for the childish mermaid to have rescued you

Every day, you would meet up with the merman and bring him fish

Walking into the isolated cove far from the ships harbor on the beach, you set down the bucket of fish & grab the sea shell to call for the mermaid few moments later, luffy the little mermaid landed on the shore resting his upper body on the sand & his long tail in the shallow water