Kotodama (DB1-EN058) - Dark Beginning 1 Unlimited

As long as this card remains face-up on the field, more than 1 monster with the same name cannot exist face-up on the field. If a monster with the same name as a face-up monster on the field is Normal Summoned, Flip Summoned, Special Summoned or flipped face-up later, it is destroyed. (If monsters with the same name are Summoned or flipped face-up at the same time, they are all destroyed.)