Black Butler is a moving and dark anime. If you want to watch Black Butler online then here are a few options (we checked these as recently as February 2019):

 

Just cancel before the 30 days is up and you don’t pay anything, simple. If you’re wanting to watch series like Black Butler for free and in high quality right now, then a free trial with Amazon Video is your best option.  

Or you can simply buy the episodes individually if you prefer.