Here is the full list of all 28 Seal Guardian achievements.
Complete chapter 1-1
Complete chapter 1-2
Complete chapter 1-3
Complete chapter 1-4
Complete chapter 2-1
Complete chapter 2-2
Complete chapter 2-3
Complete chapter 2-4
Complete chapter 3-1
Complete chapter 3-2
Max out the Health Bar
Max out the Witch Power Gauge
Learn all skills
Learn all sword combos
Learn all axe combos
Learn all scythe combos
Beat the game in 1 hit kill difficulty
Complete all chapters with S rank
Complete a chapter without continue
Complete a chapter without taking damage
Perform a 100-hit combo
Stay in the air for 30 seconds
Knock down the red demon boss
Head shot the red demon boss with a laser
Defeat the blue demon boss without using any witch statue
Break all armors of the green demon boss
Remove all the obstacles before the entrance of Witch Village
Use all the weapons in a combo