Kantan.regex has a cats module that is, in its current incarnation, fairly bare bones: it simply provides a few useful type class instances.
The cats module can be used by adding the following dependency to your build.sbt:
libraryDependencies += "com.nrinaudo" %% "kantan.regex-cats" % "0.5.3"
You then need to import the corresponding package:
import kantan.regex.cats._
The following instance for cats type classes are provided:
MonadError and SemigroupK for GroupDecoder.Functor for Regex.Show and Eq for all error types (RegexError and all its descendants).