Well, everyone in this manga has both an exceptionally high libido and exceptionally flexible morals. The character summaries in the most recent chapter were also rather interesting, particularly Rise deciding to drug the OL group on a whim and the fact that she just happened to be carrying sleeping pills around.
Also, for those who missed it, I think the mother may be part of the same company as the first group of characters, since she got out of work early, but came home late. Also, everyone seems to have connections to everyone else in this manga.