This event is exclusive to Animal Crossing: City Folk and in Animal Crossing (GCN). In the GCN game, the player will receive letters from various villagers. The more the villager likes the player, the better the gift they are given will be.
A week or two before the holiday, villagers will start hinting that they intend to send out chocolates to a special someone. Pete, the pelican who delivers the mail, also posts to the bulletin board advising players to clear out their mailbox to assure that all Valentines arrive in a timely manner.
On Valentine's Day, players will receive letters from all of the animals in their town of the opposite gender. Each of the three male or female personality types can write two different kinds of letters. Thus, each gender can receive up to twelve different Valentines from their villagers. Each villager will attach a gift to their letter. What the player receives in the mail depends on the relationship with that villager. Shirts are given for so-so to poor relationships, but furniture is given if the player and villager are good friends.
The day after the holiday, Pete will make another post saying that he is done delivering Valentines, but wonders when he will start receiving any.
In Animal Crossing: City Folk
In City Folk, the player will receive a letter from the villager that they are friendliest with. This villager is always of the opposite gender. The letter contains a box of chocolates, which can be eaten. In addition to this, if the player buys coffee from The Roost they will receive hot chocolate instead, and Brewster will wish the player a Happy Valentine's Day.