Fii-tan is about the same size and Nendoroid's and you can swap about their heads too.
At the moment Aoi-chan is looking after Fii-tan.
Sofubi no Fiitan comes with a book too with gorgeous illustrations by BB Sensei
Sofubi no Fii-tan is due out at the end of this month and will retail for 4,800 yen. A list of retailers at the end of this page.