Good or Evil?
I debated whether Reiko was good or evil for a while. Then I realized that in Parasyte, there was no good or evil. There were simply sides. This would not be the case if Reiko had not been created, however.
You see, most parasites were selfish, instinctual man-eaters who didn't care where they came from or where they were going. They killed humans when they were hungry, ate what they wanted to, and left mutilated bodies lying around everywhere. The protagonist of the story is Shinichi, and he's human, so this terrible species would have most definitely have been the villains of the story, and in a way they were. If you take Reiko out of the story, Hirokawa's cabal probably would never have come to be, parasites probably would have continued killing and eating out in the open, and Shinichi would have been killed pretty early in the story. Reiko brought the parasites together to think about their future. That left them worried about killing out in the open, and it made them work harder for food, which probably led to less human deaths. Reiko also kept the parasites off of Shinichi.
Reiko was the central element between human and parasite, and was their only hope for coexistence. She truly was in the middle of the pack, trying to understand humans and her species. Aside from Migi, Reiko was the only parasite to feel human and parasite emotions. She not only tried to get the parasites to think more human, but she tried to get Shinichi to understand where the parasites were coming from. She compared humans to cows, asking him how the parasites eating humans was any different from humans eating cows. It really is something to think about.
Many would argue that humans are a sentient species and that Reiko was evil for even bringing up the argument. Heck, I sure thought that when I first read it. Reiko does more to blur the good and evil line, though. She stops eating humans, and tries to live on normal human food. That shows a huge understanding that she had for our species, and I think it made Shinichi respect her more in the end.
Then we have the whole betrayal thing. If she was evil, why would she betray her species to help Shinichi? Why would she try to save Shinichi at all in the first place? Could it be that she had a conscience or a heart? Gasp. Shock. Horror. I would like to say so, but unfortunately all I can do is hypothesize as the story never came out and said it. She probably didn't live long enough. It's a good thing for her that she didn't live. I mean, what would have happened to her?
By betraying her species, Reiko put herself in an odd spot. Because she had killed and eaten humans, she would never be accepted by humans, and after the parasites learned what she did, she would no longer be accepted by them either. It's an interesting thing to think about. What would have happened to her if she didn't die?
Wow, a character that is accepted by neither the good side nor the evil side. What does that make her?
I like the term sympathetic villain. I like my villains sensitive and morally ambiguous. That's probably why I like Reiko so much.