[Akubinium] Shizuka-chan Can't Stop (COMIC LO 2023-10) {Mistvern}

Shizuka is the honor student every family brags about—top grades, star athlete, endless friends—with one unshakeable secret only her big brother has caught: she pees in the bath and believes nobody notices. His attempts at discipline spiral into hands-on sex-education lessons, a one-week bladder-control bet, and a breathless first time that leaves her riding him and demanding he prove she's finally an adult. But rather than curing her, every lesson only fans the flame, and now bathtime means a naked little sister who can't stop peeing—or begging for more.