Last year it was reported that Nintendo's first ever smartphone game, Miitomo, wouldn't be released at the end of 2015; instead, it was being delayed in order to promote it. Now, the free app has finally launched, but for now it's only available in Japan.

While many Nintendo fans were hoping the company's first entry into the lucrative smartphone games market would feature one of its iconic characters, such as Mario or Link, the title is a 'social app' rather than a game.

Using Miis - the user-created avatars that have been around since the launch of the Wii console - a huge part of Miitomo involves customizing your character. You can choose its clothes, personality, the way it speaks, and even how it looks using your smartphone's camera.

In addition to having in-game purchases, some outfits and special game tickets can be bought via Nintendo's new rewards program - My Nintendo - using Miitomo points, which are earned by playing the game or with real-world money. You can also use these points to get discounts on games, console themes, and other digital rewards.

Once you start the game, it asks questions as a way to get to know the user, such as "where did you go last weekend?" or "what's your favorite food?" Your Mii will then seek out other avatars and exchange answers as a way to get people into conversations.

Even though reviews of the game have been mixed, it's been well-received by early adopters in Japan and is number 2 on the Japanese iOS app store. Nintendo plans to release four more mobile games over the next 12 months; they will all be games, rather than social apps, and some will feature famous Nintendo characters.

Miitomo will be released in the US at some point in the future, but Nintendo hasn't specified when.