Must be destoyed in battle by the monster you want to banish.
You can set this card to banish it together with the monster that destroyed it. It is best to do this when your opponent only has 1 monster that can destroy it, or your opponent likes to attack with his strongest monster first.
Alternatively you can crash D.D. Assailant into your opponent's monster, taking the damage, and banishing both of them.
She could be considered an upgrade to D.D. Warrior as she can do battle without banishing herself.