Here is the full list of all 14 Bullet Witch achievements.
Maxed out all power-ups.
Cleared all stages on HARD difficulty.
Cleared all stages on EASY difficulty.
Cleared all stages on NORMAL difficulty.
Cleared all stages on any difficulty.
Cleared Stage 6.
Cleared Stage 5.
Cleared Stage 4.
Cleared Stage 3.
Cleared Stage 2.
Cleared Stage 1.
Cleared all stages on CHAOS difficulty.
Cleared all stages on HELL difficulty.
Played for over 15 hours.