The random cover story that Yuu and Mugi are related is starting to fray around the edges, but still I guess it is mostly believable. Volume 4's highlight is the appearance of a foe of Yuu, a girl who is certain that all guys are scum and when people are not, she wants to "help" them no longer hide who they truly are. For once, a romantic opponent who does not have a long term hidden crush, or has a secret hidden past? Nah, she's just mean. And by the end of the volume she has not hopelessly fallen for Mugi. Well, maybe she will in another volume, but it hasn't happened yet. In Volume 5, the interesting bit is Mugi finding a job in a restaurant so he can finally use that cooking skill that has been a running subplot so far in the book. The romantic entanglements of the restaurant just aren't interesting to me, and quite frankly smack of paternalism.
Pastel vol. 4 and vol. 5 are both available from Right Stuf, Intl., an online retailer specializing in anime and manga.