My jaw dropped. I looked down at my 16 year old sister as she stood in my bedroom looking up at me, waiting for my response to what she had just said. She had on a headband with a pair of cat ears on it, a childhood toy that she had taken to wearing a lot lately.
"Y-You want to what?" I said, not sure if I'd misheard.
"I want us to have sex," said Mia matter of factly, my nerdy brown-haired sister's expression serious and her tone formal, as if she was making a perfectly normal proposal. "I have a normal teenager's libido, but between all my homework and extracurriculars, I haven't had time to find a romantic companion. We already live together, so it's logical for you to meet my needs."
I stared at her for a long time. She was crazy, but I loved my autistic little sister. She was highly intelligent, and had always had an analytic personality and cold emotional affect, although she could be affectionate in her own way. Ever since she had watched Star Trek recently, she had been acting more and more like a Vulcan. It had seemed like a harmless quirk, until now.
"Mia, I'm your brother," I said, finally, in a voice that I hoped wasn't unkind (not that she would notice even if it was). "We can't have sex. That's incest. It's wrong."
"Wrong?" she asked, looking genuinely puzzled. "Wrong is a subjective judgment. What I propose is logical. We live in close proximity to each other, so it's simply convenient for me to use your male reproductive organs for bonding and sexual release."
My cheeks burned as I shook my head. "But...but..." Arguing against her crazy proposal shouldn't have been this difficult. My autistic sibling had always been far smarter than me, despite her social difficulties and...quirks. Once she got an idea into her head, she tended to pursue it relentlessly.
"Brother," Mia went on, using a hand to straighten her cat ear headband and speaking in a condescendingly patient adult-talking-to-a-slow-child voice, "It's futile to resist me. Taking into the account the natural male attraction to youth, I calculate that having a teenage girl's vulva envelop your penis will be at least seventy-two percent more pleasurable than masturbating to internet pornography."
She stepped towards me and I backed away, but she kept moving toward me until my back bumped against my bedroom wall and I couldn't retreat any further. She was standing uncomfortably close, her big eyes looking up at me through her glasses with total seriousness and her ridiculous cat ears bobbing slightly. I felt like a mouse being stalked by a very silly hawk.