While you control another "Noble Knight" monster, your opponent cannot target your monsters with less than 1800 ATK, except this card, for attacks or with card effects. If a "Noble Arms" Equip Spell Card is equipped to this card: Target 1 face-up card on the field; destroy that target. You can only use this effect of "Noble Knight Drystan" once per turn.
You can equip Noble Knight Medraut with a noble arms card and then destroy the equip to special summon Drystan from your deck. The destroyed Noble Arms card will then be equipped to Drystan so that you can destroy a card your opponent controls.
Being able to activate Drystan’s destruction effect during your opponent’s turn could make for some good disruption and could even be used to destroy attacking monsters. Use Glory of the Noble Knight to search your deck for a Noble Arms card and equip it to Drystan during your opponent’s turn. You can activate the effect of Noble Knight Bedwyr to equip a face-up Noble Arms card from another monster to Drystan, this effect can be used during either player’s turn.
Here is a list of Noble arms cards you can equip to Noble Knight Drystan to trigger his destruction effect.