The obedience collar certainly sounds like fun, you think to yourself. You've always wanted to have a kinkier relationship with your girlfriend, but she's been hesitant. She hasn't been entirely negative about the idea, she's just said that she has a hard time getting in the right headspace. With this little tool, you could probably get her there.
Or maybe the problem was your relative sizes. She's a large woman - not fat, but tall and muscular. Taller and more muscular than you are. If you could make her smaller, or yourself bigger... or both? Speaking to the wizard, he sees where you're going, and guides you over to a set of rings.
"These rings should be of interest for you. They enable the transfer of masculine and feminine energies between two bodies. Wear the large gold ring, and have your girlfriend wear the silver ring, and you can transfer her masculine energies to yourself, causing both physical and mental changes. The exact nature of the changes are a result of the wearers ideals, and can be controlled to a certain extent, so by concentrating you can direct the changes."
You're sold. "Oh, and one final thing. While I'm at it, why not just go all the way and get a reality warper?"
"Certainly. What would you want it to do?"
"How about setting gender roles back to how they were in the 50's?"
"An excellent choice. That one I even have at the ready here. No need for a wait while I enchant it."
You pay for the three items and head home, to find your girlfriend greeting you at the door.