Keiko · Font Options
This article offers details about the Font options in Keiko Theme. To see the complete list of theme options available in the theme go to Keiko Theme · Customizer Options
When clicking on "Fonts" in Customizer, you should be able to see these options:
From here you can choose between Handwritten, Serif or Sans-serif fonts for blog name, titles and body text. Default is Handwritten/Handwritten/Serif.