Nintendo has the most downloaded app in one of the world’s biggest markets for mobile gaming, and it’s easy to see why it’s spreading — thanks to one of its coolest built-in social tools.

Miitomo’s built-in Miifoto feature has already caught on with fans of Nintendo’s first mobile app, which is out now in Japan (everywhere else soon). Miifoto enables anyone to quickly build funny photos featuring their Mii avatars as well as their friends’ Miis. In about a minute and a few button presses, you can produce witty visual responses to a comment or a fellow Miitomo user’s post. This creates a bold separation for the app, which is essentially a social network with some light gaming mechanics, when you compare it to Facebook or Twitter.

I’ve already had a lot of fun with Miifoto. It’s my preferred way to respond to friends, and I’m clearly not alone. Nintendo has built in a sharing option into Miitomo that posts the images to Twitter with the #Miifoto hashtag. People can then click on the auto-generated link that accompanies the image, and it takes them to a landing page that tells them all about Miitomo. This seems like a great way for Nintendo to facilitate the virality of its first smartphone release as it begins launching on iOS and Android in other territories.

But beyond fueling discovering, Miifotos are just a ton of fun. I trolled through the #Miifoto tag on Twitter and gathered up some of the most popular posts so far to give you an idea of what’s possible.

Check ’em out: