Translation: View both of each character's endings
This can take awhile to do, seeing as to how each playthrough takes 20-30 minutes. Just go through every stage on level 1 and spam all the bosses with bombs and in due time, the cheevo shall be yours! At the end of each game, you will receive two choices for each character...one good ending and one bad ending. You must select each of the two choices for all six characters for the achievement to unlock. Also, be sure to sit through the ENTIRE cinematic at the end, to ensure you get the achievement.