Boku ga Boku ni Koufun Suru Wake ga Nai! ~Onee-chan no Otouto Josou Kyouiku~

"She really is something, huh... Chisa-senpai..." "I guess so..." My classmates sigh as they stare through the window at my older sister, Chisa, eating her lunch in the courtyard. Bathed in warm sunlight, she’s wearing a radiant smile, completely unfazed by all the eyes on her. There was a time when I felt just a tiny bit proud to be her little brother... "I’m home." "Welcome back—" "Augh..." "Hmm~? What’s wrong? Getting all shy just because the sister everyone adores came to greet you?" My sister grins at me as I freeze in surprise. "So, what shall we do today..?" All I can do is wait in silence for whatever she’s about to propose. The longer the pause, the more certain I am it’ll be something outrageous... "That’s right, either way, first you’ll have to strip!" There it was: the other face of my sister that only I know.