Japan isn't big on Christmas cards. In fact, unless you actually know where to look (Tokyu Hands or The Loft) you're probably going to miss them entirely. But the jigsaw cards are fun, you can write your message and then break them into dozens of pieces, pop them into an envelope and send it to your friend for re-assembly at their leisure. But the issue is not really one of Japan being a largely non-Christian country and therefor not celebrating Christmas, most Christian countries don't send Christmas cards for that reason; it's just a traditional way to say you're thinking of your friend.
And Japan does that on January 1st. In fact, more than 20% of the total mail despatched each year is delivered on one single day as the national population takes time out to wish each other well. The cards are known as nengajo and will almost always be personalised, whether with a photograph of the family (which year by year you see growing, ageing, learning, leaving the nest or just smiling and saying hello) or with a handwritten note to let you know you're not forgotten in life.
And as you get older the stack of cards grows from a few to often hundreds. I once stayed with a family for New Year in southern Kyushu and their collection required two hands to hold them all. But I have decided to become eco-friendly and make my little contribution to saving the rainforests. The card was prepared with photoshop and Facebooked and emailed. A few however will still be printed and handed personally to some who don't inhabit this digital world. Because they're also my friends and I'm thinking about them too.