@Sandwitch: the 前編 (prequel) suggests that you are right but I am perplexed. The set you linked was drawn before, this one happens after they established their relationship as the "sprites" shows the director way more lewd than in its normal state you can see pages 2-5 on the other set, and it's about the "pinch" of the director with the arrival of her little sister. Nothing goes in the direction of this one being a prequel.
That's why the short stories which comes along the sets should always be available inside the archives... :((((