Kotaro Tanaka's company Motelsworks introduced their 2018 lineup of complete bikes. The AUX:E is the 20" freestyle model for flatland and street riding. It's an affordable bike (less than 600USD) that comes with all the feature a beginner needs: freecoaster, 3pc crank, both brakes and so on. The 19,3" top tube is a good compromise for flat and street riding.
Besides the 20" version there is a 16" and even a 14" model available for the younger rider out there. Check jykkjapan.com for more details.