Everybody on here worried about the eggs or the battle plan, but they conveniently skip over the part where he just finally got confirmation that he was gang raped by his own allies and the woman he loved and was faithful to.
She put him to sleep against his will, then let multiple other people have their way with him WHILE SHE WATCHED!
Swap the sexes around and there would be boycotts for this author. But because it happened to a guy and was done by cute girls, it is completely ok. FUNNY even. And then, the author just makes some funny looks and moves on without EVER addressing the issue.
Sylphy knows that there are demi-humans being trafficked and "harvested" by human nobles and high end clergy. The thought sickens her. But she does the very same thing here to Kousuke. And you know she KNEW it was wrong because she can't look him in the eye and even started to punish him for being unfaithful while it was going on. You know, yelling at him and avoiding him and all that. So she knows she did something bad, but never says one thing about being sorry. The author brushes it off like it was a passing joke.
And I know there will be responders that think I am over reacting because the guy got some bird puss, but if you think that, then YOU ARE THE PROBLEM! If she had asked him, he would have done it. There would have been no betrayal, no feelings of wrong doing, and everyone would have been happy including the readers.
At this point in the story he should force her to address the issue of the betrayal, demand she apologize, and if she refuses then he should abandon these people. He owes them NOTHING. The only reason he did all this for them is because he loved Sylphy. And hell, some of them knew (even those apart from the Harpies) and didn't think to object. So SCREW THEM!