Fairy Tail is about to encounter some demons as the anime enters the Tartarus arc. One of the biggest arcs in terms of what is covered and fights Tartarus arc has Natsu and the others come face to face with the guild known as Tartarus as they shake there world to the core with their actions. Also these guys are demons and that makes difficult for Natsu and the others. To give you an idea of what I mean the only demon shown in the series thus far before this arc was the demon that was sealed by Gray master. The below will give you an idea what they are going for so enjoy that and the poster.
As always thank you for reading.