I accidentally put on my little sister's underwear, and of all days, that's the day we have a health checkup, so I have to somehow get through it - a violent panic otherworld edition.

Second UNKO Cup (Organized by Kyono Unko-san "Tsuredzure ww" https://ncode.syosetu.com/n5438et/) I'm participating in "A violent panic where you accidentally wear your little sister's panties and happen to have a health checkup that day, so you have to somehow get through it"! In the otherworld I was transferred to, there was an absurd rule that you absolutely must wear your little sister's panties for health checkups... However, I don't have a little sister since I was transferred here! But there was a loophole in the school rules that said "step-sisters are acceptable too"! I'm somewhat anxious about whether this follows the rules, but let's just say it's good enough!