Complex sentence: Rather, characters gain Enhancement Points (EP), which can be gained by destroying enemy units and beating missions, to be spent on either buying skills or upgrading to a higher level and its skill set.
Split into simpler sentences: Rather, characters gain Enhancement Points (EP) to spend on skills and upgrades. EP is gained by destroying enemy units and beating missions, which can then be spent on either buying skills or upgrading to a higher level and its skill set.