Suck-ubus

Mark and his girlfriend Yvette were falling deeply in love, but after a month of dating, Mark still hadn't received more than a chaste peck on the cheek. In as nonconfrontational a manner as he could, he asked her why she was being so chaste.  Oddly, she handed him a bright red lollipop and told him to lick it while she explained.  Mark was confused, but the lollipop was delicious and he wasn't about to refuse Yvette anything.

"I'm in love with you, Mark, and I want to spend eternity with you," she explained. "But I have a confession to make. I am a succubus, and any sexual contact I have with a mortal will drain their essence and make me more powerful. However, I have decided that you are the one, so I infused that lollipop with pure demonic ichor. You should be feeling the changes by now. You're going to become my twin sister. Now we can make love safely and hunt the mortal realm together...forever!