There is just one -category, namely the truth value True. Compare the concepts of (−1)-category (a truth value in general) and 0-category (a set). The point of -categories is that they complete some patterns in the periodic table of -categories. (They also shed light on the theory of homotopy groups and n-stuff.)
For example, there should be a -category of -categories; this is the true truth value. The category of -categories is a monoidal category in a unique way; then a category enriched over this is a -category; such is necessarily an enriched groupoid. If you think of a -category as a 0-poset, then this makes a -category a (−1)-poset. If you think of a -category as a (−1)-groupoid, then this makes a -category a (−2)-groupoid.