As far as I can tell these transformations are just a fancier Buy/Sell/Craft Shop that you sometimes see in Giran.
Generally useless unless you plan to AFK vend on your character a lot.
All weapon boxes give a random item.
Feather is removed at the end of this event.
It is a one use item.
Fighter Pirate Fruits
in General Classic Discussion
Posted
According to the released patch notes, they will not be deleted after the event.