This doujin pick up right where the previous chapter left off: Saki was having some wild sex with her boyfriend when her (equally well endowed) little sister Shiki walks in on them. Luckily for her, the couple don’t notice her, so she manages to hide and watch them go at it.

But since Shiki is as pervy as her sister, she starts touching herself while peeping. Of course she eventually gets discovered and of course she ends up in a threesome. What did you expect?
*All characters depicted in this work of fiction are adults, regardless of their visual representation or textual description, and are not based on any real person*