All Kobo's ignore font-family when they are included in the body CSS style. Some ePub that have embedded fonts turn them on via font-family in the body CSS style.
To me, this is a major bug. The only way to fix things so they work is to put the font-family in other CSS styles. I'm wondering though if a styled div could work like so...
<div class="font">
the chapter goes here
</div>
.font {
font-family: charis
}