During each of your End Phases, destroy this card unless you send 1 'Iron Core of Koa'ki Meiru' from your hand to the Graveyard or reveal 1 Beast-Warrior-Type monster in your hand. Once per turn, you can reveal 1 'Iron Core of Koa'ki Meiru' in your hand to Special Summon 1 Level 4 or lower 'Koa'ki Meiru' monster from your Deck, except 'Koa'ki Meiru Urnight'.