One downside to the bloodlust skill is that it is a passive skill, that sole reason is something that makes the skill itself unpredictable, even for the holder of the skill. Someone like Dustin that has a cold blooded nature will find it hard to utilize this skill as he won't always show killing intent when he kills. He just swings his sword because he has to or because there's a reason to, and not because he harbours a deep feeling to kill. This in turn also means that it's a perfect skill for his type of person since he has some level of control over it.
Either way, such a skill can be trained and mastered to the extent that the holder of the skill holds a high decision on when they want to release the skill, making it a strong weapon in some cases.
(A/N: I use blade to refer to sword-like weapons that are not swords, e.g sabres).
