[Update] Nintendo's trying to boost Miitomo's popularity with a Splatoon-themed event
Splatter up
Nintendo is pushing out some Splatoon-themed event right now for Miitomo and some of that is going to require your action via Twitter.
In order to increase the app's popularity, Nintendo is asking people to retweet a message containing a hashtag. The goal being, of course, to trend and bring Miitomo to people who didn't know it existed.
On top of that, Nintendo's also bringing some Splatoon gear in its pachinko inspired minigame Miitomo Drop. But you'll also be able to unlock some with Miitomo coins and platinum coins inside Nintendo's account system.
You'll be able to unlock an Inkling boy wig and Inkling girl wig and more next tuesday.

The twitter event is expected to last until April 26.
[Source]