Ane ga Boku no Seieki Tsuki Pantsu o Haku Wake

"I love my sister. I really love her. I want to… have sex with her." That’s the kind of straightforward desire the protagonist, a younger brother, has. Every day, he pours his liquid lust into his sister’s panties, somehow managing to keep his sanity intact. "It’s wrong that siblings can’t have sex…" Then, one day, his sister—a struggling illustrator—gets an unexpected job offer. "Eroge character art." Wait, what?! Illustrations of men and women in lewd situations? No way he’s letting that happen! …Wait, hold on. Isn’t this actually… a chance to do something nice with his sister? [Translated from dlsite]