Haku

According to the released patch notes, they will not be deleted after the event.

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.