What about the "Black Isle Plaster" - heals all your injuries 1/rest?
What would be easiest and won't interfere with ingame 3D-models and stuff would be a weapon with the usual appearance, but a different set of colors and/or materials.
So, things like an obsidian sabre, stiletto, dagger or rapier would fit the pirate theme best. But on the other hand that's also pretty boring stuff - unless you'd come up with some really creative combination of the usual enchantments (because new, unique ones we make up will also not be implemented).
So... the shape of the item can't be too different from items which will be in the game (but we don't know which weapon types and shapes will be in, erm...). Great situation that!
What about a wooden sword with the shape of a "usual PoE2 sword", no matter what that fial shape will be, but the edge is made of obsidian, fused into the wood. This would not require a different 3Dmodel but only an easy texture change where the inner blade apperes brownish and the edge is jet black. Maybe also some obsidian inlays. It's a mystery how the creator of this blade was able to craft obsidian in this way, but the sword is light and supersharp (for example - come up with other enchantment ideas please).
Could still be of Huana/animancy/shamanistic origin and might have onve been a weapon of revenge - the Huana shaman of a nearly extincted or enslaved tribe wanted to kill raiders/colonists/whatever with a weapon which looked like the ones they brought into the Huana world, but which consisted of the materials his tribe used and was infused with the magic of his tribe. Was also used to execute and sacrifice a lot of captured foreigners to their god(s). Maybe Skaen in a different appearance got int otheir heads at some points. Something like this.
I also really like the idea of putting an ability onto this item like the Girdle of the Driving Wave gives you Knockdown or the Siegebreaker Gauntlets give you Cleave and so on.
Because of that, and the possible backstory/lore I still like the idea of putting Blood Thirst on the weapon (= 0 recovery after kill). This would best fit to a slower, two handed weapon. So I think I'll vote for melee weapon made of obsidian.