DD's ranking map is, as always, unlocked by clearing out all the story maps. It's a 15 turn long map where you get points for meeting various objectives, and your highest scoring run is counted for ranking purposes.

So, here we are. First ranking event for EN GFL. Arctic's ranking event is probably the easiest and most boring of the ranking events. The goal for these ranking events is to get a high score on the hidden map of the event. Points are gained by defeating various enemies that spawn in the map, however, you lose points for repairing or losing any units. Thus, to put it simply, to get a high rank you need to kill as much as you can without any losses or repairs.