Ah, the foreshadowing. Kanade was complaining about how awful it would be if her sister was found by a vampire, and then she was! Not that anything bad happened to her, rather it was all a warm fuzzies ending to this episode, as this show tends to have.
We finally get to see some supernatural powers in this episode when Erika tries to chase down Kuze, who is revealed to be a different sort of supernatural being. It all comes to an end when Hina is sees two people jumping around the woods like superman, and thinks that is her some reason her sister. She sees Erika in vampire form, and all the action comes to a screeching halt as the have to deal with the crisis of ‘will they or won’t they’ erase Hina’s memory of having seen her vampire self.
To be honest, I can’t see the logic behind letting Hina keep the memory. Yes, erasing her memory sucks, but by all logic, it’s too risky to let just anyone who happens upon it know either. The consequences if it leaked out—well, to say the least, would not be pleasant. There would be a lot of freaking out, and everyone would be out to kill the mostly harmless vampires.
I think Erika’s choice in the end just demonstrates her desperation to be human and have friends that she is willing to put herself at risk. To be that lonely…is really sad.