"I think my engagement might be cancelled... because of my insensitivity..."

After school, my sister-in-law, Nikaido Kikuno, came to me for advice. It was obvious from the fact that her engagement was decided at a young age, but the Nikaido family was a distinguished family, and in the past, Kikuno was kidnapped by degenerates for ransom. She seemed to have become insensitive due to her trauma at the time.

I didn't want any trouble, but this was my sister-in-law... I couldn't just ignore her. So, I thought about it and tried to mess with her just like usual. That's right, just like I normally do.

"If your private place became insensitive, then you can increase your erogenous zone sensitivity by another method. Anal... In other words, your anus."

"M-M-M-M-My anus! Onii-sama, how filthy...!"

She didn't like it at first, but I couldn’t help but grin and gloat at Kikuno’s determination to do it for the sake of her engagement. She really is... an easy woman to handle.

"...So, what should I do...?"
"Take off your underwear and get on all fours on that bed."

Then, lying on all fours face down on the bed in the nurse's office, Kikuno did as I instructed. She raised her upper body, and thrust her hips up.

"Onii-sama, I beg of you. Please... treat my condition."

[Based on MTL of DLSite's description.]