Placing these previews in a bit of speculative context:
Akira wakes up to Sana crawling on him. While "entertaining" her, Chika walks in. She storms off, and Sensei gets up to follow, only to bump into Ayane, who shoves him into a stall to service him. Chika has cooled down, and comes back to talk to Sensei, walking in on him with Ayane. She wanders off to sulk, where a very tired and satisfied Sensei finds her and talks to her, and he then wanders off to go bed....only to accidentally stumble into Yumi's bed.
Hilarity ensues.