There is no marker designated as a “headings” marker for footnotes. \fk and \fq are markers that are checked by the “Quote check” of basic checks. If the word is not found exactly as it is written in the text then Paratext will display an error.
One option would be to use either the \fl marker (for a label) or the \fqa marker that is actually for alternate quoted material, but isn’t checked by the basic checks.
Another option would be to use a character style (+em…+em* or +it…+it*). While these are discouraged if a more appropriate marker is available, in this case where no specific marker exists, it could be used. So, you would have something like this:
\f + \fr 1:0 \ft \+em Leviler\+em* Mabetteki \f*
Note that the “+” is needed since the em is nested in a footnote.