This is probably way too late to say this, but I just realized that Eve (the Zombie) seems to have the personality that Ririsu used to have as a young girl, but more grown up. As opposed to the actual, more warped personality Ririsu developed due to the trauma of being able to see first love zombies. In a sense, I think that Eve could be seen as an alternate version of Ririsu that could've been. If things work out a certain way, Ririsu might even slowly become like Eve over time too.