Well, GRPC is language-agnostic, so you have GRPC APIs for any language that supports GRPC (which is pretty much all of them). It runs on the same port as HTTP, so just connect to the same place you run your regular API calls.
Here is the documentation for the GRPC api
https://www.ory.sh/docs/keto/reference/proto-api
And you can generate your grpc client code (which I strongly suggests you do, only insane people would write it manually) from the proto files found here:
https://github.com/ory/keto/tree/master/proto/ory/keto/relation_tuples/v1alpha2
(Not sure if these are mirrored from someone, or if this is the single source of truth)
Good luck!