This is a story-related achievement and cannot be missed. It will unlock upon defeating Vikke, the Stage 2 boss. Vikke is very easy to defeat however you will have to dodge quite a bit here.
Phase 1 - Attack him from the back and dodge often and you will have no issues. If he flies up to his perch shoot him down by holding down then pressing.
Phase 2 - Once you cut him in half you will have to fight his upper and lower body as separate enemies. Defeat his Upper Body to move on to his 3rd phase.
Phase 3 - His third phase will be against his giant head. Dodge and attack him when he stops moving. Using your Chainsaw Blaster will be extremely useful for this phase.
Chainsaw Blaster bullets can be found around the edge of the ship. Once you have defeated the head the achievement will unlock.