It's Not Sex If I Don't Put It In, Right Sis?

From DL site: Hanahito has an older sister, China, who is sweet and cute. Hanahito harbors unspeakable feelings toward his sister and worries that he'll get busted rubbing one out to her sleeping face while she naps. One day, he walks in on China taking care of herself. What will her response be when he says "Let's do it together"...⁈ *they aren't actually related, but these two have no idea.