Hear me out, Gaz as a siren and Makarov as a pirate captain. He's one of the most feared pirates out there, but one day at night as he’s looking over the ship’s railing, he sees a siren. They quickly dive down after noticing him, but eventually the siren begins to slowly trust that Makarov isn’t going to try and hunt him. But at some point, the siren disappears. With the disappearance, it is announced that Gaz, a witch that has aided pirates (especially to get back at the Crown for persecuting witches, hunting sirens and other mythical creatures, etc.) is now back in business. Makarov has been wanting to get a meeting with Gaz, and luckily they’re near the cove the witch inhabits so he goes to meet him and Gaz agrees to work with him. Gaz also is known for being raised by sirens, so he knows a lot. At some point on their journey, Makarov starts asking a bunch of questions about sirens to Gaz. At first, he thinks that Makarov wants to hunt sirens like some do, but he instead wants to try and court a siren(???), but the siren he wants to court hasn’t shown up. He’s asking all these questions like what do they eat, migration patterns, rituals, etc. Gaz asks him to describe the siren to see if he can maybe tell where the siren is from/which pod they belong to, and lo and behold Makarov describes Gaz’s siren form. So Gaz decides to transform one night and slip into the water to see if he can see Makarov. And they trade silly little rituals, though the siren never surfaces to speak (since he doesn’t want to give it away). And so they have a little ritual, Makarov and Gaz discuss things about sirens (and he starts slipping in little things that he likes) in the day, and during the night, the siren comes out to play around in the water. Makarov slowly takes notes, and once when docked, he comes across a fish that Gaz mentioned sirens love (actually, Gaz loves that fish, it reminds him of his home. Different pods have different kinds of fish they feed on), and buys one and gives it to the siren. He watches the siren eat it (yes he very much likes it, he thinks it’s cool and also somewhat hot watching the siren tear into the fish), and they seem to have really enjoyed it. At the same time, he also starts developing a crush on Gaz and starts to notice the similarities (similar canines, similar glint in their eyes, etc.).Â
Eventually, Gaz gets found out after he drags himself aboard this ship, slowly turning back into his human form. Makarov comes across him and it leads to a confession and kiss (also, Makarov takes Gaz back to the captain’s quarters to help wipe off the lingering blood and scales from the transformation). And they rule the seas (no TF141 in this au) since there's a siren witch and a powerful pirate. Also, they torment the Crown with their chaos :)