Miko is playing everyone like a damn fiddle. Being an actual normalfag in a cadre of otaku is dangerous.
Saku is the purest character in this manga. He's constantly shown as out of the loop with the sexual machinations of the other three, is the little dick in the cuck/bull dynamic, and has a raging NTR fetish. Even Amane being horny for him sounded like small penis humiliation dialog. It also seems Miko is using him to trigger MC-kun's monster cock mode, since MC-kun gets incredibly aggressive with sexual competition.