Just in case anyone wants to know: Episode 4 corresponds to volume 24 (out of 37.... soon to be 38) of the manga. So there's at least enough manga for one more season after this one. The manga has been progressing very, very slowly (volume 37 came out in 2013, volume 38 came out in 2016 for japanese, and July 2017 for english) with the story not even close to being finished. Hopefully with this anime, the manga will start to flow more readily so we can see an end to the story.