If this is, indeed, a trilogy, then we will probably never get to explore what caused the eponymous inversion of the leads' personalities. Personally, I am more interested in that character development than in whatever tryst they may be having. I am guessing Saika has had some kind of traumatic experience after graduation, which dampened her spirits, -- maybe a death of a close relative, or some kind of big failure in college or at work? But what kind of transformative experience turned the social recluse Ukawa into a prowling alpha lesbian?
EDIT: wishful thinking
for ch2 or too much of a spoiler?
Wait, you mean the whole encounter of the close kind didn't happen? But there does seem to be something written on the back of her hand on this page?