Jake felt that he shouldn't let them escape… the goal of those guys was still mysterious, but Jake was determined to get on their way, so he used dark flames on those guys. The range of that skill had increased a lot recently, so it worked. When the boss heard its allies getting hurt, it turned around to check things, and Jaked used that chance to attack. There was no point in hiding the dark flames anymore, so he enhanced his blade with it. It was also better to finish things as quickly as possible...