[Matsuyama Seiji] Joshikai de Yotte Otouto ni Mukae o Tanonda Asa... Nazeka LoveHo de Otouto to Ita Shita Ato de Bikkuri na Ukkari Onee-san... Ase [Red Eye] [DLSite] [Translators Unite]

After one too many drinks at a girls' night out, a curvy older sister calls her little brother to pick her up—only to wake up in a love hotel with hazy memories of the sweaty, record-breaking night they apparently shared. Once she gets a hands-on refresher of his perfect-fit endowment and the sheer volume he produces, any lingering regret evaporates fast as she eagerly drains him again before dragging him toward the station. Walking home together, the flustered pair trade blunt confessions and strike a scandalous deal: until he finds a real girlfriend, onee-chan will keep him thoroughly satisfied—as long as mom and dad never find out.