I think a pirate or ship captain who brings goods from neighboring towns and countries could kind of be interesting. He or she would be like the travelling merchant but could maybe have a different set of items only obtainable trough them like seeds, furniture, or other goods. Maybe it could also add in a trading mechanic to try and spice up the mid-late game? The captain could travel to different places every week and the player needs to try and figure out what items sell for high values in that location. They would dock for 2-3 days but unlike the traveling merchant, you are able to befriend them in order to learn about their backstory
If I had to design them I would go for a blunt female pirate named Alice who left her home, a small port town in the Gem Sea, because of the conflict the war brought over it. She became a pirate in order to restore her homeland and take back what both the Ferngill Republic and Gotoro Empire stole from her