Well, I suppose it was a secret that just couldn't be kept forever. Really, it was only a matter of time before he found out, and rather than hearing it from her mouth...He actually witnessed it happening. And she, too, realised that he saw everything.
That ending really encapsulates that one moment where everything just falls apart, huh...
Oooof. I hope we'll get a sequel where it'll have a Vanilla ending. But I doubt it. (Don't get me wrong. I've read some manga/visual novels in the past with NTR that turned to Vanilla, but it's very rare for it to happen.)
That ending really encapsulates that one moment where everything just falls apart, huh...