Oh! From the beginning we were told one of us was not actually part of us, and they were from an organization that kidnapped us. They were thus the traitor.

And it is true, she was part of the organization that did kidnap us, and took our memories. But, those people weren't wrong. Thus, the traitor was the only good person on the entire island!

In fact, at first, I thought the traitor would have been Hinata kun. I had been really hoping that would be the case. But, Nanami san is alright too, if it couldn't have been Hinata kun.