Gungnir brought a new elemental system to the table, foreign to the one used in all previous episodes thus far. There are now five (5) elements. Below is a chart showing how they interact with eachother.
As seen above, Fire/Earth are in opposition to Water/Wind, meaning they will inflict bonus damage to enemies with the opposing element. Null, however, receives no such benefits, and will inflict consistent damage regardless of elemental alignment. A unit's alignment can change depending on the equipment in their possession as well as the terrain they are standing in.