Popularity Level

A Mii's Popularity Level is one of the two experience levels in Miitomo. Your popularity level goes up as you gain more friends and receive more hearts and comments on your questions and answers. You also get experience through posting Miifotos and getting hearts and comments on them. There doesn't appear to be a maximum to how much experience you can gain in a day, unlike with your Style Level.

Levels and Rewards
You're rewarded with a unique title and either a ticket or hat item for leveling up. As with Style Level, there is currently a 50 level cap. Below is a list of rewards and titles earned through leveling. Experience earned depends on the task. Each heart received earns you 3 experience while each comment grants you 2 experience. However, only the first heart and the first comment of the day from a single user will be counted towards the experience total.