Kenichi threw away his porn. His digital collection, suspicious DVDs, adult manga, eroge, even browser bookmarks. all of it was gone. He had been shocked that his imoutos were repulsed at his interests, so he had decided to give up his otaku hobbies. For his imoutos, he will become a responsible onii-chan!
On the other hand, his imoutos were pained, not knowing of their onii-chan's decision. They felt guilty that they had hurt him beyond their imagination just by teasing him a little bit. As a replacement for his porn, they will offer themselves to him instead!