Koisuru Succubus no Ikenai Jijou

Kou Takeuchi is a healthy able-bodied AV actor living with his two step-sisters, Horuu Akumeru and Ouna Akumeru. However, the sisters also have a secret: they are both succubus. To one day fullfill their dream of marrying Kou, both sisters aim to become human, by absorbing lust without cumming over one whole day to collect seven Kintama balls which will grant them their wish. However, after one month of absorbing Kou's lust, both sisters have only collected one Kintama ball, as they sabotage each other in hopes of being the first to become human and marry Kou. (Source: Takeshobo, translated)