Here is the full list of all 16 One Day : The Sun Disappeared achievements.
Helmet Collector
Mace Collector
Spear Collector
The World Savior
Sword Collector
Axe Collector
Boots Collector
Shield Collector
Defeated the King of Giants
Defeated the King of Fiery Spirits
Defeated the Merman Boss
Defeated the Scorpion King
Defeated the Boss Ogre
Defeated the Goblin King
Dagger Collector
Armor Collector