You could simply decide to conjure a sword.<br/><br/>Depending on the quality of the sword, it would be taxing on your demon (with a Conjuration stat of 3, you can conjure lesser items without draining mana).<br/><br/>You don't actually have to ask him to provide the energy. The energy is channeled through your link. He needs to actively focus to block the energy.<br/><br/>If you give him reason not to trust him, and then try to cast a spell, you might not yet want to describe the spell's effect, because if you give him reason to block it, he might block it before you cast it.