She Was Actually My Stepsister summary:

A little brother-like secret relationship with his little sister!? A romantic comedy between siblings with a misunderstanding begins!Akira, my stepbrother, was brought into my life as a high school student after my parents remarried. He is a cute boy but shy because of the complicated family environment he grew up in. I had a crush on my brother, so I always spent time playing with Akira for his sake…. He loves me… We hit it off, and the distance between us grew rapidly! I asked him,"......Brother, do you like me by any chance?""Of course I do."The misunderstanding between the two of us deepens. And finally, I realized that Akira was my "sister" and I was confused..."I like the distance between my brother and me as we have always been. I'd rather be with you more than I am now."Akira's approach to me, aiming to make us "lovers" instead of "siblings," has begun!A flirtatious romantic comedy with a little sister who is too cute and carefree to be a brother! Official Light Novel: https://fantasiabunko.jp/special/202111jitsuimo