The Valentine's Event is an event introduced by Riako on 8/Feb/2015. In this event, you are given the option of sending special cards to other users with messages.
If you manage to send and receive at least one card before the event ends (14/Feb/2015), then you have the chance of receiving a special event Pokemon.
These cost 50 Sweet Hearts each, and can be sent either anonymously or not. In addition to that, messages may be sent to your closest friends or complete strangers.