Malenti

You were born a sahuagin in the Eternal Dominion of the Thunder Sea, but ritual magic and the blood of the kar'lassa allowed you to consume and replace a surface dweller. You can never regain your original form; for all intents and purposes, you are who you appear to be. You're physically indistinguishable from them, and you have enough of their memories to fool even their family and friends. But you have the mind of a sahuagin, and you're loyal to the Dominion.
As a Malenti, the first question is why the Dominion chose to replace this particular person, and how your mission relates to your activities as an adventurer. It's possible that your only mission is to observe the dryskins and occasionally provide information to a sahuagin spymaster, or you might have a specific goal that drives your actions during your adventures.