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 WATER monster in your hand. Once per turn, you can send 1 "Iron Core of Koa'ki Meiru" from your hand to the Graveyard to return 1 Spell Card from your Graveyard to the top of your Deck.