[Taishinkokuoh Anton] Imouto datte Tsukatte Ii no yo? (COMIC Penguin Club 2021-04)

When her father is away, a young woman named Onii-chan discovers her younger brother's untouched panties and gives in to a forbidden curiosity, pinning down her inexperienced brother to take his virginity herself. The shy sibling, overwhelmed by the sudden intimacy of her straddling him, gasps through his first climax as she confesses, "I like you, Onii-chan" and proposes a twisted arrangement: "from now on, let's not do it as siblings." The story culminates in a breathless, tender resolution as she smiles softly and declares, "Let's do it as... lovers," transforming their taboo encounter into a raw declaration of forbidden romance.