The Feast of the Winter Star occurs on the 25th of Winter. The event works like a secret Santa, where a random villager will be selected to give you a gift, and you selected to give one to a random villager. A week (18th) beforehand, Mayor Lewis will send a letter telling you who your gift recipient is. On the 24th, the mayor will send the player another letter, reminding them who they're supposed to give a gift to.
Willy explains the origin of the Star, if the player opts in to listen.
Festival of Ice • Feast of the Winterstar