Protect the lamp, and compromise on the perception.

Ruby proceeded to sit against the nearby tree as Yang straightened up, shrugging off her jacket, then pulling her crop top off to expose her boobs. She then sat on Ruby's lap, allowing her to idly play with her tits. "Hmmm, so if I wanted to protect the lamp, I would need something fairly airtight, right?" Ruby asked.

"Mmm, indeed, Mistress. It's something pretty much anyone would covet. Who wouldn't want me as their willing sex slave?" Yang purred, caressing Ruby's hands with her own as they ran over her bust.

"That's for sure," Ruby nodded. "Hmm, can I wish for the ability to know where it is at all times, and conjure it in my hand at will?"

"That's not sexual, Mistress," Yang moaned, before giving a little yelp as Ruby gently pinched and pulled her nipples.

Ruby just grinned. "What, a motive to keep a sexy, magical slave isn't enough?"

"...retracted," Yang chuckled. Ruby made the wish, and once Yang granted it, she added, "Okay, that just leaves our relationship... We going to keep it secret, or do you wanna use a wish to let everyone know I'm your slave?" she asked.

Ruby considered as she continued to casually fondle her topless sister. "... let's go with somewhere in between. I wish it was completely acceptable in everyone's minds for us to be in a sexual relationship, despite us being sisters. We can also be pretty open about the fact that you're incredibly submissive in bed," she ultimately decided.

"Works for me!" Yang nodded, snapping her fingers and granting that wish as well. She turned towards Ruby with a smile, and kissed her, Ruby returning it gladly.