Koisuru Succubus no Ikenai Jijou

Synopsis & Lore

The twins, Oona and Hooru, are housemates who come to the house of Takeuchi Kou, a super-skilled porn star. They are just normal girls but they're actually not. In fact, they are succubus who devours human sexual desire. The reason they are in Takeuchi's house is to be with their beloved Takeuchi Kou. However, the succubus can't fall in love with a human because of their species barrier. In order to make this possible, there was a way for a succubus to become a human. That is... To collect abstinence balls that can be obtained through abstinence. In order to get the abstinence balls, they pull each other's legs, make each other come, and interfere with each other, and the abstinence survival battle begins (Source. MU)