Shortly after my father remarried, I found myself spending more time alone with my new stepsister. She was usually quiet, sitting at the kotatsu studying, but one day she suddenly dozed off, giving me the perfect chance to play a prank. When I peeked under the kotatsu, I saw her sleeping soundly in pure white panties. Overcome by temptation, I reached inside and began directly stroking her pussy. The sensation was too intense—she woke up and asked, "Onii-chan, why are you doing this?" She didn't resist strongly, just seemed slightly surprised. Flustered and desperate for an excuse, I panicked and impulsively kissed her. In that instant, the handjob session began. Though she gasped, "Onii-chan, we're siblings!" she didn't push me away. Instead, as I forcefully pulled her panties off, her body responded eagerly.