The Dark Lord shared. "The green volume over there is written in parseltongue, so you will have to concentrate if you want to give it to your bibliophile witch. It might be easier for you to read it yourself. It explains energy conversion and concentration for rituals and such. An incubus survives on sexual energy. That's just another flavour of life-force. If you can adopt one of the spells, you might be able to feed your little incubus, without actually fucking him. You're at a boarding school after all. I'm sure there is energy to spare."