The Mystic Knights of Tir Na Nog/WMG

Power Rangers Samurai is the Spiritual Successor of this series
Both series are similar in the aspect of Elemental Powers and the rangers assigned to them. Furthermore, since the second sequel was cancelled, it can be surmised that Midar and Nemain not only have nefarious plans for Kells and Tir Na Nog, but also the entire world. They retreated to Japan, and under the Sanzu River, they formally established the Nighlok group.