You get this by almost getting hit (sparks fly off your ship).
Here is the best method that I have seen from Laorik (he used RFJ but I was told it can be done on RF2 with the same ship):
"Using training mode on RFJ again, boost your fighters and bombs number to 99 and choose fairy as a character. Set enemy fire to 100% and difficulty to expert. Then go into the last, level Real Battle phase 2 + Final Boss, and simply move to the back of the map and just constantly press the bomb button. While Fairy's is in her bomb shooting mode, she actually absorbs bullets for points and they count for the almost master achievement. It took me about 1 1/2 playthroughs of the level to get Almost Master."