As soon as Shiki sees Akiyo peeping through the door (page 8, panels 5-6),
he immediately switches position with Chinatsu in order to give Akiyo a full
view of the action (page 9, panel 1). Quick thinking on his part.
"I was only supposed to come here to work at this island guest house."
Silly Shiki-kun, you don't know H-scenarios very well, do you? Plus it's a sure bet bet that a Mother (Akiyo-san) "Knows" what's been going on, but that also her own long-dormant urges would get re-awakened.
Prepare yourself for having unlocked the "F.F.M." route. Do Not Resist ... It Is Your Destiny (You Lucky Bastard ... GRR)!